Muhammad Ali teamed with Joe Frazier to form the greatest rivalry in boxing history.
In sports like baseball, hockey and basketball, the best teams meet in postseason series to decide who advances and moves on.
It's not a one-shot deal. A team must win a best-of-five or a best-of-seven series.
In boxing, a fighter will meet a rival and then move on to the next fight. However, if the first fight is uniquely special or popular, a rematch may occur.
Once two fighters meet each other more than once, they have developed a rivalry.
These rivalries are often memorable for their overall quality.
In this piece, we look at the greatest rivalries in boxing history.
Sugar Ray Leonard and Roberto Duran engaged in three bouts during their rivalry.
The first was by far the best, the second was the strangest and the third was a bout between two aging fighters that were nowhere close to the top of their game.
In the first fight in Montreal in 1980, the sharp boxing of Leonard was apparent in the early rounds, but as the fight progressed, Duran was able to turn it into a street brawl and win the unanimous decision.
The pair met five months later in New Orleans and Duran tried to engage Leonard in another brawl. He was unable to do that and called off the fight with his infamous "No Mas" decree in the 8th Round.
Duran was never able to recover from that defeat and his reputation suffered badly. They would meet in a third fight in 1989 in Las Vegas and Leonard won a unanimous (and somewhat boring) 12-Round decision.
Muhammad Ali and Ken Norton fought three times between 1973 and 1976.
Norton was a huge underdog in their first fight in San Diego, and there was every reason to believe that Ali did not take him seriously.
However, the powerful and muscular Norton broke Ali's jaw in the early rounds and Ali fought the rest of the bout in pain—and shockingly lost a split decision.
While Ali would take the decision in the return bout and also also the third fight, it was Norton who won admiration because of his ability to stand in with Ali and compete on nearly even terms.
Sharp-punching Aaron Pryor met superb boxer Alexis Arguello for the light welterweight title in Miami in 1982.
Arguello dictated the pace of the fight with his hard, accurate punching; but Pryor's power eventually took over and he wore down his man. The end came in the 14th Round when Pryor won by TKO in an action-packed fight.
Pryor and Arguello met again in Las Vegas in 1983. It was more of the same, but Pryor asserted himself earlier and knocked out Arguello in the 10th Round.
Riddick Bowe and Evander Holyfield met in three Las Vegas bouts between 1992 and 1995.
This was a series that featured the heavy-handed Bowe against the all-around skill of Holyfield. Holyfield was the better boxer, but he was really a pumped-up cruiserweight. Bowe was a full-scale heavyweight who had power in both hands.
In the first fight, Bowe won a close but unanimous decision. In the second meeting, Holyfield won a majority decision, with two judges giving the edge to Holyfield while the other judge called the bout even.
Finally, Bowe asserted himself in the third bout and came away with an 8th-Round technical knockout.
Ray Leonard and Thomas Hearns met in one of the most anticipated bouts in 1981 for the world welterweight championship in Las Vegas.
The fight was billed as the boxing skill and artistry of Sugar Ray Leonard against the vicious punching of Thomas Hearns.
Hearns had the better of it through much of the fight when Leonard's trainer Angelo Dundee leaned in and told Leonard that he was in the process of losing the fight: "You're blowing it, son, you're blowing it."
Leonard responded and ended up securing a 14th-Round TKO over the rubber-legged Hearns.
The rematch would occur eight years later in Las Vegas. This was a close fight that went the distance, with most ringside observers believing that Hearns won the fight. However, the fight was ruled a draw as one judge called it for Hearns, one for Leonard and the third called it even.
Few fighters have ever put on the show that Tony Zale and Rocky Graziano put on in their three-fight rivalry from 1946 through 1948.
Zale, from Chicago, went to Yankee Stadium and knocked out the Brooklyn-born Graziano, in the 6th Round.
They met a year later on Zale's home turf at Chicago Stadium in one of the greatest brawls of all-time. Graziano registered a 6th-Round TKO.
Zale had dominated much of the fight, pounding huge lumps all over Graziano's face as the New Yorker took a tremendous beating. However, Graziano kept punching and when the 102-degree heat in the stadium weakened Zale, Graziano pounded him relentlessly until the fight was stopped.
After the fight, Graziano uttered his famous line (via ESPN.com), "Hey, Ma, your bad boy done it. I told you somebody up there likes me."
In the third and final bout in Newark, New Jersey's Ruppert Stadium, Zale leveled Graziano with a 3rd-Round knockout.
The three battles between Arturo Gatti and Micky Ward were comparable to the exciting and legendary bouts between Tony Zale and Rocky Graziano.
None of the Gatti-Ward fights in 2002 and 2003 were for a boxing championship, but the two fighters displayed so much strength, skill, determination and guts that the three bouts are often considered among the best ever.
Ward took the first fight with a majority decision. He used furious body punching to carve out his win. Gatti took the final two fights with unanimous decisions. The two went at each other in all three fights with relentless fury.
The first fight was named the fight of the year by Ring Magazine (via BoxRec.com) and so was the third fight.
The three fights between Muhammad Ali and Joe Frazier were among the most exciting in boxing history.
The first occurred at Madison Square Garden in March, 1971, and it was the most hyped event of the sports year.
Ali, the boxer, had the edge in the early rounds, but Frazier, the slugger, took charge in the late rounds. It was a close fight going into the final rounds, but Frazier registered a 15th-Round knockdown and won the decision. The victory allowed Frazier to retain his heavyweight championship.
Frazier would lose his title to George Foreman, so when Ali and Frazier met in 1974, there was no championship at risk. Ali won a unanimous decision in the fight.
They met again in 1975 in Manila. Ali had knocked out Foreman and he was the defending champion. In this bout, Ali's speed and sharp left jab gave him the edge in the early rounds, but Frazier's explosive left hook and battering-ram style had hurt Ali badly.
Just as it looked as if Ali had nothing left, he turned it around in the late rounds and Frazier's corner stopped the fight after the 14th Round because he no longer could see Ali's punches.
An exhausted Ali could hardly get up off of his stool when he found out he had won the fight and the greatest rivalry in boxing came to an end (via CNNSI.com).