Like other tournaments, tennis at the Olympics follows seeding protocol. Of the 64 players entered into the draw, 16 of the top-ranked competitors are seeded in both the men's and women's fields.
Then the unseeded players are placed randomly throughout the draw. The main reason for the seeding is to prevent the top-ranked players from meeting in the tournament during the early rounds.
Seeding ensures the later matches will remain competitive, assuming the lower-ranked players are eliminated, leaving the top-ranked players to meet each other in the final rounds.
It would not be good planning if the the top 10 players faced each other in the first round, for example.
Regardless of the "plan," however, sometimes the seeding goes awry because an unseeded player wins over someone ranked higher. This is an upset. This also makes tournaments unpredictable and exciting.
Already in 2012, the No. 6 seed Tomas Berdych was upset by Belgian Steve Darcis in the first round. Following that upset on day one, Agnieszka Radwanska found herself down and out after German Julia Goerges defeated the No. 2 seed, also in the opening round of action.
Like other tennis events, Olympic competition has seen its fair share of upsets since 1988, when the sport returned to the Olympics held in Seoul.
Following are the 25 biggest upsets at previous Olympics since tennis re-emerged as a part of the Summer Games.
Tim Henman, seeded No. 7, was upset by Karol Kucera of Slovakia in the first round in the Sydney Summer Olympics in 2000.
Henman, for whom Henman Hill was named outside Centre Court at Wimbledon, played the role Andy Murray has assumed for the British—he who will capture the next Wimbledon crown for the British Empire. Like Murray to date, Henman never made that goal come true.
Still, the Brit was a top-ranked serve and volley tennis player—one who never won a major.
Henman also never managed to play his best tennis at the Summer Games, and Sydney proved to be no exception to that fact. Previously, he was excused in the second round during the Atlanta Games in 1996, even though Henman did win a silver medal in doubles.
The Brit had his chances to win his opening-round match, but never took advantage of his break points early on. This gave Kucera the courage and the confidence to come back strong and win the match 6-3, 6-2.
Henman, who had hoped for so much, came away empty again in men's singles competition, upset in round 1.
For the Williams sisters and for former gold medalist Venus Williams, seeding really meant very little because both sisters battled hard in major tournaments and at the Olympics—finding a great deal of success throughout most of their careers.
In 2008, Venus seemed to be marching through her portion of the draw without much difficulty. She put aside Timea Bacsinszky of Switzerland 6-3, 6-2, followed by a victory over Iveta Benesova of Czechoslovakia 6-1, 6-4 in the second round. Victoria Azarenka of Belarus was Williams' third round opponent, losing 6-3, 6-2.
Events were progressing nicely until Williams met Li Na in the quarterfinals. Venus fell in two tough sets 5-7, 5-7, sending the lady from China through to the semis, where she lost to Dinara Safina 6-7, 5-7.
Venus Williams recovered from her loss, teaming with sister Serena to win a gold medal in women's doubles, which eased the pain of this quarterfinal upset.
Seeded No. 6 at the Summer Olympics in Beijing, Andy Murray was shocked in the first round by Lu Yen-hsun playing for Chinese Taipei.
Lu defeated Murray in straight sets 7-6, 6-4. He went on to advance past Agustin Calleri of Argentina in the second round before falling to Jurgen Melzer of Austria in round three.
For his part in 2008, Murray was finished before he got started in men's singles competition.
Today, he is hoping for more. In this year's Olympics, Murray won his opening-round match at the All England Club against Swiss Stanislas Wawrinka 6-3, 6-3.
Murray's next round will find the Brit doing battle with Jarko Nieminen of Finland, seeking to avoid another upset.
In 2004, nothing seemed to bode well for team USA's women at the Summer Olympics in Athens.
Prior to the start of the event, top seeds Jennifer Capriati and Serena Williams pulled out at the last minute, leaving team leader Zina Garrison without time to replace them.
Then, during the third round, unseeded Mary Pierce of France upset the No. 6 seed Venus Williams in straight sets 6-4, 6-4.
No woman would bring home a singles medal from the 2004 Olympics for the first time since the Olympics reinstated tennis as a sport in 1988. Venus was the gold medal winner in 2000.
Mary Pierce, for her part, would advance to the quarterfinals, where Justine Henin-Hardenne would send her home. Henin-Hardenne became the 2004 gold medal winner for the women.
During the Summer Olympics in 2004, unseeded American Mardy Fish upset the No. 5 seed, Juan Carlos Ferrero of Spain, in the second round.
Upsets became the order of the day for the tennis competition during the 2004 Summer Games, at least on the men's side of the draw.
Ferrero, ranked world No. 1 in men's tennis in 2003, saw illness and injuries begin to take a toll on his career and his ranking.
The upset by Fish in the early rounds of the Athens Olympics added to the Spaniard's losing efforts during the early matches of the season.
Fish would go on to enjoy great success in Athens, making it to the finals, where he fell to eventual champion Nicolas Massu of Chile, winning a silver medal for his efforts.
The No. 5 seed Boris Becker was upset by Marc Rosset in the third round in Barcelona in 1992.
But the big German should not have felt alone since Rosset upset many top seeds on his way to a gold medal in Barcelona in 1992.
During the men's competition, all but Goran Ivanisevic of the men's top 10 seeds were gone by the quarterfinals in Barcelona in 1992.
Rosset alone took out the No. 9 seed Wayne Ferreira of South Africa in the second round as well as the No. 12 seed Emilo Sanchez of Spain in the quarterfinals before eliminating the No. 4 seed Goran Ivanisevic of Croatia in the semifinals.
To compensate, Becker teamed with countryman Michael Stich to win gold in doubles, giving the Germans their share of precious medals from Barcelona.
In 1988 at the Summer Olympics in Seoul, Korea, Henri LeConte of France was the No. 4 seed behind No. 1 Stefan Edberg, No. 2 Tim Mayotte and the eventual champion, the No. 3 seed Miloslav Mecir.
Since 1988 marked the first year since 1924 that tennis was part of the official Olympic program, the fans in Seoul were eager for their countrymen to do well.
In one of the biggest upsets of the year, Kim Bong-soo, 25, of South Korea stunned fourth-seeded Henri Leconte 4-6, 7-5, 6-3, 3-6, 7-5 in less than four hours.
Leconte was ranked 12th in the world, while Kim held down the No. 361 ranking.
Highly-favored LeConte was sent packing by Kim in the second round in Seoul.
As a hometown boy, the South Korean received much support from fans that day. His joy at winning was obvious to all, as the young Korean celebrated on court.
LeConte, however, was far from pleased at being booed by the assembled crowd.
With the Olympics being held in Sydney, Australia, in the year 2000, the No. 4 seed Lleyton Hewitt entered the men's singles competition with a great deal of hope and expectation.
But the Aussie was unexpectedly knocked out in the first round by Max Mirnyi of Belarus.
It was a shock for Hewitt and his team, but Mirnyi played a better match on the day. He deserved the win over his teenaged doubles partner, Hewitt.
The Australian had hoped for much more playing in his home country.
Like many before Hewitt learned, the Olympics can produce unexpected results and surprise winners.
Max Mirnyi lasted until the quarterfinals, when he was ousted by German Tommy Haas 6-4, 5-7, 3-6.
Wildcard Leander Paes of India upset the No. 3 seed Thomas Enqvist of Sweden in Atlanta in 1996, 7-5, 7-6.
Paes would go on to meet eventual gold medalist Andre Agassi in the semifinals, while Enqvist was sent home after his third-round loss.
Much was always expected of Enqvist by his home country and by the tennis world.
In 1995, Enqvist was presented the ATP's Most Improved Player of the Year award. The Swede was expected to follow in the footsteps of tennis legends Bjorn Borg and Stefan Edberg. Although he never quite rose to those heights, Enqvist did win five tour titles in 1995.
He was, naturally, hoping to do better at the Summer Game in Atlanta, but suffered an unexpected loss from an unseeded player.
On the other hand, Paes enjoyed a sensational run in 1996.
Pete Sampras, the third-ranked player in the world, was upset by Russian Andrei Cherkasov in the third round in Barcelona in 1992.
Barcelona, of course, was played on clay where the Sampras serve and volley style of play proved not to be nearly as effective as on grass and hard courts.
Finding himself losing in the fourth set, Sampras let it go, preferring instead to start fresh in the fifth set.
Unfortunately, that decision did not pan out. Sampras double-faulted to let Cherksasov go up 5-3 in the fifth set.
From there, the Russian served it out. Sampras lost 7-6, 6-1, 5-7, 0-6, 3-6. The last American male in singles tennis went home.
Cherkasov lasted until the semifinals in 1992.
The No. 4 seed Elena Dementieva upset the No. 3 seed Serena Williams in the quarterfinals in Beijing in 2008.
For most people, this would not be considered much of an upset. On the day, however, it was a major surprise.
As usual, Serena Williams was one of the favorites coming into competition in women's singles in Beijing, but the Russian Dementieva was playing some of her best tennis throughout the singles competition.
Dementieva would eventually win the gold medal in women's singles in 2008.
After losing, Serena turned her attention to doubles, where she won the gold medal with her sister Venus, just as the sisters had done in 2000 in Sydney.
In 2004, Nicolas Massu of Chile won the singles title in a series of tournament upsets almost unequaled in Olympic history.
Further, after winning in singles, the No. 10 seed teamed with countryman Fernando Gonzalez to win the doubles—the first competitor to win gold medals in both events since American Vincent Richards in 1924.
The singles competition at the Olympics in 2004 was marked with numerous upsets in the early rounds. Tim Henman, the No. 4 seed, was dismissed in the first round, as was Juan Carlos Ferrero, the No. 5 seed. The biggest upset came when No. 1 seed Roger Federer went out in the second round.
Continuing his march through the draw, Massu met and defeated the No. 3 seed, Carlos Moya of Spain, in the quarterfinals, winning 6-2, 7-5. Naturally, Moya was expected to be the one to turn back the man from Chile—but he didn't possess enough weapons on the day.
Mardy Fish, who was not seeded, survived to make the finals. Massu met the American to compete for the gold medal.
The 2004 Olympic final went the distance, with Massu emerging with a gold medal in a five-set victory, 6-3, 3-6, 2-6, 6-3, 6-4.
In 2004, at the Olympics held in Athens, Andy Roddick of the USA was the No. 2 seed behind Roger Federer, who was seeded in the top spot.
Men's tennis at the Athens Olympics was turned upside down by upsets of the top seeds in the early rounds.
Among them was Andy Roddick, who lost in the third round to Fernando Gonzalez of Chile 6-4, 6-4. Gonzalez played inspired tennis throughout the Games.
The Chilean was seeded No. 16 at the Summer Games and would go on to make it to the semifinals before losing to Mardy Fish.
This was not only a bad year for top seeds, it was a bad year for American tennis in general, except for the play of unseeded Mardy Fish.
The big-serving American Roddick expressed his disappointment at losing early, but moved on to the U.S. Open.
Li Ting and Sun Tiantian of China won that nation’s first gold medal in tennis in 2004 by upsetting the No. 2 Spanish team of Conchita Martinez and Virginia Ruano Pascual.
The Chinese ladies took the Spaniards by surprise, winning 6-3, 6-3. Li and Sun were definite underdogs coming into the match.
The Chinese duo, however, took advantage of every short ball that came their way and made the Spanish team pay dearly for, perhaps, underestimating them.
The celebration of the Li and Sun was memorable, as they ran around the court with the Chinese flag draped over their shoulders.
The duo soon became national heroes in China.
The No. 2 seeds in women's doubles, Conchita Martinez and Arantxa Sanchez Vicario, were upset in the second round by Olga Barabanschikova and Nadia Zvereva of Belarus at the 2000 Summer Games in Sydney.
Longtimes staples on the women's doubles tour, the Spaniards were upended by the ladies from Belarus, who were unseeded at the Games.
Zvereva would go on to become a doubles champion teaming with Gigi Fernandez—but in 2000, teaming with her countrywoman, she upset the No. 2 seeds.
The ladies from Belarus lasted until the semifinals, when they lost to Kristie Boogert and Miriam Oremans of the Netherlands.
In the end, the pair from Belarus came away empty-handed after losing their consolation match for a bronze medal.
No. 2 seed Stephan Edberg was upset by unseeded Russian Andrei Chesnokov in the first round in Barcelona in 1992.
The Barcelona summer Olympics became more like a tennis landslide for the top-seeded men, who were buried after the first few rounds. The clay courts may have had something to do with it.
The player hit first and hardest was the No. 2 Swede Edberg, who was demolished by the Russian 6-0, 6-4, 6-4, winning a mere eight games in total.
The ecstatic Russian was elated by his upset of the No. 2 seed. He would go on to win one more match before falling to eventual silver medalist Jordi Arrese of Spain in the third round.
Meanwhile, Edberg returned home to Sweden.
Seeded as the No. 1 team in men's doubles at the 1992 Summer Olympics in Barcelona, John Fitzgerald and Todd Woodbridge were upset in the second round by the Indian team of Leander Paes and Ramesh Krishnan.
In fact, none of the top three seeds in men's doubles made it to the final round, with the No. 1 seeded team going out first.
Leander Paes and Ramesh Krishnan would lose in the next round to the Croatian team of Goran Ivanisevic and Goran Prpic.
Eventually, India would see a surge in success in men's doubles.
Unseeded Venus and Serena Williams upset the No. 1 seeds, Amelie Mauresmo and Julie Halard-Decugis, in the quarterfinals at Sydney in 2000 in women's doubles.
The Williams sisters had begun their doubles career earlier that year in Wimbledon, winning the title there, but lacked the total points to be seeded at the Olympics.
After dispatching teams from Canada and Russia, the unseeded Williams sisters from Team USA took out the No. 1 seeds convincingly, 6-3, 6-2.
Serena and Venus Williams would go on to win the doubles event, defeating the team from the Netherlands, Kristie Boogart and Miriam Oremans, in the final.
Venus, of course, would capture the gold medal in singles as well.
2008 turned out to be a very trying year for soon-to-be world No. 2 Roger Federer.
The Swiss was dominated by Rafael Nadal at the 2008 French Open. Then, trying for his sixth consecutive Wimbledon title, Federer went down to defeat as Nadal captured his first Wimbledon trophy.
Earlier than expected losses at the Rogers Cup and Cincinnati would see Federer lose his No. 1 ranking to Nadal in August prior to the start of the U.S. Open.
Federer, however, felt that winning Olympic gold could salve some of the wounds he suffered earlier in the summer—but that also did not happen.
In Beijing during the 2008 Olympics, Roger Federer was upset in the quarterfinals by American James Blake 4-6, 6-7.
The singles competition ended for Federer, but he would team with countryman Stanislas Wawrinka to win the gold in doubles.
Sebastien Lareau and Daniel Nestor, seeded No. 4 in Sydney, upset the No. 1 seeds, Todd Woodbridge and Mark Woodforde, in the Olympic finals in Sydney in 2000.
On paper, granted, this does not seem like much of an upset, but the Aussie team was appearing in their final Olympics in front of their hometown fans. The crowd was eager for the "Woodies" to capture gold one more time.
The pair had combined for 11 major titles and 61 world tour championships from 1991 to 2000. They held the record for most doubles titles until it was matched by Americans Bob and Mike Bryan.
The "Woodies" were accorded the distinction of being named the ATP Doubles Team of the Year six times throughout their career playing together.
They won one French Open title in doubles, two Australian and two U.S. Open titles, as well as a record six doubles titles at Wimbledon.
But in 2000, playing in front of their home crowd in Sydney, the top-seeded pair fell in the gold medal match, losing to Sebastien Lareau and Daniel Nestor of Canada, 7-5, 3-6, 4-6, 6-7.
Marc Rosset of Switzerland upset the No. 1 seed Jim Courier in the third round in the 1992 Summer Games in Barcelona.
But then Rosset defeated everyone in his path that year as he went on to capture the gold medal in 1992 on the clay courts.
Every man seeded in the top eight was gone after the third round, except Goran Ivanisevic, who made it to the semifinals.
Rosset was unseeded. Courier was the No. 1 player in the world, winner of the French Open and Australian Open in 1992. Yet the American could win only seven games from Rosset going out 6-4, 6-2, 6-1.
American men were dropping like proverbial flies on the clay in Barcelona as the upsets continued to roll.
Unseeded Nicolas Massu and Fernando Gonzalez of Chile won the gold medal in men's doubles in 2004, upsetting everyone in their path on their way to the podium.
The No. 1 seeds, Bob and Mike Bryan of the USA, lost to this team in the quarterfinals 5-7, 4-6.
Then, the Chilean pair defeated the Croatian team of Mario Ancic and Ivan Ljubicic to send themselves into the gold medal match.
In the finals, Massu and Gonzalez defeated the German team of Nicolas Kiefer and Rainer Schuttler 6-2, 4-6, 3-6, 7-6, 6-4 in a monumental final.
When the dust settled in 2004, Nicolas Massu and Fernando Gonzalez had won a gold medal.
The No. 3 seed, Jennifer Capriati, upset the No. 1 seed, Steffi Graf, to win the gold medal at the 1992 Summer Olympics in Barcelona.
Graf, of course, won the gold medal in 1988 in Seoul, and most expected the German to repeat in 1992.
Jennifer Capriati became the youngest woman ever to win a gold medal. She was just 16 years and 132 days old at the time.
In the quarterfinals, Capriati sent home the No. 7-seeded Anke Huber of Germany with a victory of 6-3, 7-6. The teenager faced veteran Arantxa Sanchez Vicario of Spain in the semifinals, winning 6-3, 3-6, 6-1.
After defeating the No. 2 seed, Capriati next faced the No. 1 seed Steffi Graf in the gold medal match.
The 16-year-old astonished the tennis world, as she won the match 3-6, 6-3, 6-4 to take home a gold medal.
It was an amazing result for the young American, who never repeated her feat or enjoyed Olympic glory again.
After reaching the semifinals unseeded at the 2000 Summer Games held in Sydney, Roger Federer entered the Athens Olympics in 2004 as the No. 1 seed.
He had high expectations for a gold medal in 2004.
Unexpectedly, however, Roger Federer was dispatched by unseeded Tomas Berdych in the second round, 4-6, 7-5, 7-5.
Berdych would advance to the quarterfinals, where he was finally eliminated from competition by Taylor Dent.
For Federer, it was a huge disappointment, representing one of the Swiss' rare losses in 2004. He won three out of four of the major championships as he compiled a season record of 74-6.
Federer did not lose another match in 2004, but remained disappointed by this upset, losing to the Czech teenager in Athens.
Fabrice Santoro of France upset the No. 1 seed, Russian Marat Safin, 1-6, 6-1, 6-4 at the 2000 Summer Games in Sydney.
No one enjoyed playing the unorthodox Santoro, whose soft touch and deft shot-making abilities drove the opposition crazy at times.
There was no one more easily upset in those days than the volatile Russian, whose temper explosions on-court were legendary.
The match with Santoro on that day was a day filled with big Russian temper tantrums, as Safin crushed his racquet during the second set.
The man who had just defeated American Pete Sampras at the U.S. Open and who had ascended to the No. 1 ranking was brought to his knees by the diminutive Frenchman, whose smile did nothing to assuage the Russian bear.
It was a momentous upset. But then Santaro had won all five of his matches against Safin. So who is to call this an upset?