Lennox Lewis went in to the fight as the undisputed heavyweight champion of the world, having defeated Frans Botha, David Tua and Michael Grant in a two-year period of heavyweight domination. Hasmin Rahman on the other hand had fought few boxers of note.
Lewis compromised his build up, filming "Ocean's Eleven" in Las Vegas and arriving late to his South African training camp. On fight night it showed, the champ knocked out in the fifth round with a huge right hand from Rahman, who walked away with IBO, IBF and WBC heavyweight titles.
When you start your career with 89 wins and a draw, you'd be forgiven for fancying yourself as the favorite. That was the position Julio César Chávez found himself in when he squared up to Frankie Randall in Las Vegas on the opening night at the MGM Grand.
Randall had other ideas. After a seven-year stint on promoter Don King's undercards, Randall seized his opportunity, knocking the champion down for the first time in his career in the 11th round. A closely fought contest hinged on two low blows from Chávez, who was docked two points, swinging the split decision (116-111, 114-113, 113-114) in favor of the challenger. Al Bello /Allsport/Getty Images/FIle
Heavyweight champion Liston had a record of 35-1 and was a brutal physical presence in the ring, registering 15 knockouts in his previous 17 fights. Clay may have had an Olympic gold medal, but he was a fresh-faced 22-year-old and first-time challenger; a heavy 7-1 underdog going into the fight.
On the night the champion could not handle Clay's pace and resorted to skullduggery, putting liniment on his glove and temporarily blinding Clay in the fourth round. The challenger rallied after the setback, retaking control of the fight and forcing Liston to bow out on his chair between the sixth and seventh rounds. Central Press/Getty Images/file
Mayweather would contest the point, but for many "Sugar" Ray Robinson was the best boxer to ever set a foot into the ring. His glittering career was not without its hiccups, however.
Journeying to London with a record of 128-1-2, few reckoned Randy Turpin stood a chance against the American. But blessed with confidence and indefatigable spirit the Brit let fly his jab and kept the dancing feet of Robinson in check, claiming the middleweight crown after 15 rounds. Central Press/Getty Images/file
Tarver vs. Jones Jr. Part II came after a tightly contested fight in which Jones Jr. emerged the winner. Many within the boxing community expected the margin of victory to be wider this time -- with Jones Jr. chief amongst them. But things didn't quite work out for the IBO, WBC and WBA champion, who was leveled in the second round by Tarver with a one-punch knockout.
The career of Jones Jr., a man considered one of the world's greatest pound-for-pound fighters, would never recover. Jed Jacobsohn/Getty Images/file
People thought Ali was past it. People were wrong.
The fight dubbed "The Rumble in the Jungle" was pushed back seven weeks after Foreman suffered a cut to the brow during training, but entering the ring he was still the favorite among critics, if not the crowd.
In the baking heat of Zaire, Ali discovered the ring's canvas was too soft and lacked any spring. He reasoned it would be too energy-sapping to go in with his normal style, and so resorted to a tactic he later dubbed "rope-a-dope." Ali soaked up Foreman's attacks, offering little counter-punching until he knew the champion was suitably sapped. In the eighth round, after a particularly bruising exchange, Ali pounced, KO-ing an exhausted Foreman and claiming the WBC and WBA titles. AFP/Getty Images/file
Until Bernard Hopkins' career renaissance, George Foreman was the undisputed comeback king of boxing.
Foreman was coming off the back of a loss; he had not held a world title since "The Rumble in the Jungle" with Ali, twenty years previous. Moorer was the IBF and WBA champion and at his peak, slick and devilishly quick.
For 10 rounds Moorer ran Foreman ragged, with the elder statesman of the ring unable to land a punch. And then -- in the words of HBO commentator Jim Lampley -- "it happened." A huge right hand landed flush on Moorer's jaw, breaking his mouth guard and sending the champion straight to the canvas.
At 45 years old Foreman was the oldest heavyweight champion the world had ever seen, whilst laying some demons to rest in the process.
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Holmes had won 48 on the spin when he squared up against Michael Spinks. Both were undefeated, both held titles, but as a light heavyweight stepping up a category Spinks was considered the bookies' underdog.
Spinks' size disadvantage didn't seem to hamper his performance, and across 15 grueling rounds he outboxed Holmes to a unanimous decision victory (145-142, 145-142, 143-142,) walking away the lineal champion and the first light heavyweight to ever successfully step up a division.
The fight itself wasn't an upset -- the result was. Pacquiao went into the ring favorite and performed as such, throwing and landing with a higher volume of punches than his American challenger.
However, after twelve rounds the judges announced the fight in Bradley's favor, winning by a split decision (115-113,115-113, 113-115). It was Pacquiao's first defeat in four years and chaos ensued. The result was queried and judges from the WBO reviewed the fight, with an independent committee agreeing Pacquiao had won -- not that they could officially reverse the result. The Filipino would have to wait two years before his revenge, eventually winning by unanimous decision in 2014. Kevork Djansezian/Getty Images/file
Klitschko had defended his WBO heavyweight title five times before stepping into the ring with underdog Sanders, a South African with few stand out names on his boxing record.
What was supposed to a routine victory became something of a nightmare for Klitschko, who was knocked down in the first minute of the first round. A second knock down followed, then in the second round a third, then a fourth. The champion was put out of his misery by the referee, Klitschko left face down on the canvas and pondering how it had all gone so wrong. Andreas Rentz/Bongarts/Getty Images/file
"Buster" Douglas was responsible for what is seen my many as boxing's single greatest upset.
In 1990 the journeyman from Columbus, Ohio challenged Mike Tyson having only fought for a title once in his career -- a loss to Tony Tucker for the IBF Heavyweight strap. Tyson was in imperious form, undefeated in 37 fights and holder of the WBA, WBC and IBF titles.
Douglas' mother had died during his training camp and he entered the ring a heavy 42-1 against, with many casinos not even allowing bets to be placed. However the man from Ohio dominated, closing Tyson's left eye in the fifth round. Tyson rallied with a knockdown in the eighth, but was floored by Douglas in the 10th, flat out and unable to recover, the first and most shocking defeat of his career.