It was a good year for tennis stars. Famous names such as Rafael Nadal, Novak Djokovic and Serena Williams ruled the 2013 tennis season.
But that doesn't mean it was a straightforward year. Far from it. Marion Bartoli won one of the wackiest Wimbledons ever, precocious teenagers on the WTA tour defeated Grand Slam Champions and Roger Federer found himself confronting his humanity time and time again.
In other words, there were definitely some memorable upsets. Let's take a look at the eight upsets that kept us on our toes in 2013.
The first round of the U.S. Open kicked off with a shock, as 17-year-old American Victoria Duval stunned 2011 champion Samantha Stosur with a 5-7, 6-4, 6-4 victory.
It was qualifier Duval's first Grand Slam win, and the fact that it took place in front of a jam-packed Louis Armstrong Stadium as day turned to night made it that much more memorable. Duval captured the hearts of America with her aggressive game, big-time smile and inspiring back story.
Ranked No. 296 at the time, Duval's victory over No. 11 seed Stosur is the biggest upset rankings-wise on the list—it would be higher up on our countdown if it wasn't for Stosur's history of erratic play.
While most of America was sleeping through the night, an American star of the future defeated the superstar of the present in the quarterfinals of the Australian Open when 19-year-old Sloane Stephens took out Serena Williams 3-6, 7-5, 6-4.
Ranked just No. 29 at the time, this victory took Stephens into her first Grand Slam semifinal and sent overwhelming favorite Serena Williams home early at the Australian Open for the second year in a row.
The victory lost a bit of luster due to Serena's twisted ankle and subsequent back injury that occurred during the second set, but it was still inspiring to see a young American step up on a big stage.
Back in May, 21-year-old Grigor Dimitrov shocked then-No. 1 Novak Djokovic when he took out the Serb 7-6 (8-6), 6-7 (8-10), 6-3 in the second round of the Mutua Madrid Open.
Djokovic was coming off of his big upset over Rafael Nadal in the Monte-Carlo Masters and trying to hold on to his top spot for dear life.
Meanwhile Dimitrov, who has often been dubbed "Baby Federer," had been considered the Next Big Thing on the ATP tour for years but had never been able to finish up a big win.
The only upset on this list that didn't take place at a Slam, this match was a memorable look at the vulnerability of one of the top stars and the potential that the future has to offer.
Sharapova's loss to 20-year-old qualifier Michelle Larcher de Brito of Portugal in the second round of Wimbledon kicks off the All England Club portion of the list.
Ranked No. 131, the diminutive Larcher de Brito, known more for her shriek than her serve, hadn't won a match on the WTA tour all year coming into Wimbledon, while 2004 champion Sharapova had been on a tear, going 35-5 with two titles.
But the Russian couldn't find her footing on the slippery grounds of Wimbledon and fell victim to a power-hitting underachiever from Portugal, jump-starting one of the most infamous days in Wimbledon history.
Nobody bothered to tell German Sabine Lisicki.
No. 23 Lisicki, who always plays her best tennis at Wimbledon, put on a phenomenal showcase of power and resiliency as she took out the heavily-favorited Serena 6-2 1-6 6-4 in the fourth round.
Having swept through the clay-court season and winning her first French Open title in 11 years, Serena just seemed to run out of gas and Lisicki seized the day.
Lisicki's fairytale run continued to the final where she was brought back to earth by Marion Bartoli. But still, few will forget Lisicki's shock on that Manic Monday.
Roger Federer came into the 2013 U.S. Open in the worst form of his career and he certainly wasn't expected to win the tournament.
But after he made it through the first week, everyone had assumed that it would be Rafael Nadal who took out the five-time U.S. Open champion in the quarterfinals.
Unfortunately, Federer didn't even make it there. In a fourth-round match that was moved from Arthur Ashe to Louis Armstrong due to rain delays, the No. 19-ranked Spaniard Tommy Robredo—who was 0-10 against Federer in his career—shocked the Swiss legend convincingly in straight sets.
We've seen Federer have off days over the past decade, but he always managed to get through them. On this day he just never found that second gear.
Rafael Nadal arrived at Wimbledon on a 22-match winning streak. Since coming back from his knee injury, he had made the finals of all nine tournaments he'd entered, winning seven of them.
With two Wimbledon titles to his name, many expected the transition from clay to grass to be flawless.
People certainly didn't expect Steve Darcis, No. 135, to take Nadal out in the first round. But that's why they play the game.
The 29-year-old Belgian played the match of his life, blasting a lackluster Nadal right off the court in a stunning 7-6 (4), 7-6 (8), 6-4 victory.
Darcis ended up having to pull out of the tournament after that match with a shoulder injury and wasn't a factor the rest of the season, but his first-round Wimbledon upset will live on in history.
On the evening of the first Wednesday at Wimbledon, the tennis world was already reeling from Jo-Wilfried Tsonga, Rafael Nadal, Maria Sharapova and Victoria Azarenka (among others) being out of the tournament.
Still, nobody saw this one coming.
Defending champion Roger Federer was coming off of his first title of the season in Halle, and he carried his legendary streak of 36 straight Grand Slam quarterfinals into the tournament.
Sergiy Stakhovsky, meanwhile, was ranked No. 116 and had only won five ATP matches all year.
But the unheralded Ukrainian served-and-volleyed his way into tennis folklore that Wednesday and gave the crowd at Wimbledon's Centre Court the shock of a lifetime by taking out Federer 6-7 (5), 7-6 (5), 7-5, 7-6 (5).
It wasn't the end of Federer's career, but this upset certainly felt like the end of an era.