The biggest boxing upsets remind us why the sport captivates millions. Boxing loves its invincible champions, building fighters into mythic figures who seem destined to reign forever. Then someone nobody believed in throws a punch that changes everything.
Boxing upsets resonate differently than upsets in other sports. There are no teammates to blame and no bad bounces. Instead, there are just two fighters and a moment where the impossible becomes reality.
These are the biggest boxing upsets that define the sport’s history.
Buster Douglas over Mike Tyson (1990): The Biggest Boxing Upset Ever
This remains the biggest boxing upset in sports betting history. Not just boxing. All of sports.
Mike Tyson was 37-0 with 33 knockouts. He was the undisputed heavyweight champion, a terrifying force who had destroyed everyone in his path. He had knocked out Michael Spinks in 91 seconds. Consequently, he was considered invincible.
Buster Douglas was a talented but underachieving fighter. His mother had died 23 days before the fight. He was such an afterthought that many sportsbooks did not even offer odds. Those that did listed Tyson as a 42-1 favorite, according to historical records. It remains the longest odds for a heavyweight title fight in modern history.
The fight took place in Tokyo on February 11, 1990. Few American viewers watched live.
Douglas boxed beautifully, using his jab to control distance. Tyson, unprepared and overconfident, could not find his rhythm. In the eighth round, Tyson knocked Douglas down. He rose at nine.
Tenth round: Douglas landed a right uppercut followed by a four-punch combination. Tyson went down. He fumbled for his mouthpiece, tried to rise, and failed. The count reached ten.
The image of Tyson on the canvas, searching blindly for his mouthpiece, remains one of sports’ most iconic moments. The invincible champion had been exposed. Douglas had done what nobody believed possible. This is the essence of the underdog betting philosophy: invincibility is an illusion.
Hasim Rahman over Lennox Lewis (2001)
Lennox Lewis was the best heavyweight of his era when he faced Hasim Rahman.
The British champion had unified the major titles and was looking past Rahman toward a massive payday against Mike Tyson. Rahman was a late replacement, a solid but unspectacular fighter given little chance. Lewis was a 20-1 favorite.
Lewis trained at altitude in South Africa but arrived late, reportedly distracted by filming a cameo in Ocean’s Eleven. Rahman, from Baltimore, had arrived a month early and acclimated properly. Lewis looked sluggish, overconfident, and underprepared.
Fifth round: Rahman landed a straight right hand. Lewis fell face-first to the canvas, unconscious before he hit the ground.
The knockout was devastating and total. Lewis had been stopped by a punch he never saw coming. Rahman became champion, though Lewis would avenge the loss with a knockout in the rematch seven months later.
The upset illustrated boxing’s fundamental truth: one punch changes everything, regardless of skill differential. Understanding why fading the public works means recognizing that overconfidence creates opportunity.
Leon Spinks over Muhammad Ali (1978)
Muhammad Ali was 36 years old and looking for one more chapter when he faced Leon Spinks.
Ali had regained the heavyweight title by beating George Foreman in Zaire. He had survived three brutal wars with Joe Frazier. Now he faced Spinks, a 24-year-old Olympic gold medalist with only seven professional fights and a 6-0-1 record.
Spinks was a 10-1 underdog. Ali was the greatest of all time, and Spinks had never fought beyond 10 rounds in his brief career.
The fight went 15 rounds in Las Vegas on February 15, 1978. Spinks, younger and hungrier, outworked Ali from start to finish. The aging champion could not match Spinks’ energy and aggression. Two judges gave Spinks the decision in what was actually a fairly one-sided fight.
Ali lost his title to a fighter with only eight professional bouts, the shortest span in heavyweight history. The upset was as much about Ali’s decline as Spinks’ rise, but the result shocked the world. Ali won the rematch seven months later, becoming the first three-time heavyweight champion.
Andy Ruiz Jr. over Anthony Joshua (2019)
Anthony Joshua was boxing’s golden child when he stepped into Madison Square Garden.
The British heavyweight held three of the four major titles. He was undefeated at 22-0, powerful, and marketable. His American debut was supposed to be a coronation, a showcase before bigger fights.
Andy Ruiz Jr. was a late replacement, brought in after the original opponent Jarrell Miller failed a drug test. Ruiz was out of shape, overlooked, and dismissed. He was approximately an 11-1 underdog (+1100 on most sportsbooks).
Third round: Joshua dropped Ruiz with a left hook. It seemed the fight would end as expected. Then Ruiz got up and dropped Joshua. Twice. Joshua rose but was never the same fighter that night.
Seventh round: Ruiz dropped Joshua twice more. The referee stopped it. Ruiz fell to his knees in disbelief. He was the first heavyweight champion of Mexican descent.
The upset was one of the biggest boxing upsets in heavyweight history in decades. Joshua, so carefully constructed as an unbeatable force, had been exposed by a fighter who was not supposed to belong in the same ring. Joshua won the rematch by decision six months later, but the aura was gone. Ruiz had proven that Joshua could be hurt and stopped.
Evander Holyfield over Mike Tyson (1996)
After the Douglas loss, Tyson rebuilt. He went to prison, came back, and worked toward regaining the title. Evander Holyfield, a former heavyweight champion, was considered past his prime.
Holyfield had lost twice in his previous four fights and had been stopped by Riddick Bowe. He had heart problems that nearly forced his retirement. At 34, he opened as a 25-1 underdog against the still-fearsome Tyson, though heavy betting on Holyfield moved the line significantly by fight time.
Holyfield refused to back down on November 9, 1996. He met Tyson’s aggression with his own, bullying the bully from the opening bell. Tyson had no answer for Holyfield’s pressure and heart.
Eleventh round: Holyfield hurt Tyson badly with a sustained assault. The referee stopped the fight. Tyson, stopped for only the second time in his career, had lost to a fighter everyone had written off.
The rematch produced the infamous ear bite, but the first fight was the upset. Holyfield proved that Tyson could be outworked and overwhelmed by a fighter who refused to fear him. The sportsbooks took a devastating loss that night, as the public betting trends had created enormous value on the underdog.
Oleksandr Usyk over Anthony Joshua (2021)
After the Ruiz loss, Joshua rebuilt and reclaimed his titles. He was favored to retain them against Oleksandr Usyk, a former cruiserweight moving up in weight.
Usyk was a unified cruiserweight champion but undersized for heavyweight. Joshua had the size, power, and experience advantage. He was the betting favorite in front of his home crowd at Tottenham Hotspur Stadium in London.
Usyk outboxed Joshua for 12 rounds on September 25, 2021. His footwork, hand speed, and ring intelligence were clearly superior. The decision was unanimous.
The upset was less shocking than Ruiz but perhaps more significant. Usyk was not a short-notice replacement having the night of his life. He was simply better, and he proved it again in the rematch with a split decision victory. Usyk went on to become undisputed heavyweight champion.
The Buster Douglas Aftermath
Douglas’ reign lasted eight months. He lost his first defense to Evander Holyfield, knocked out in three rounds after coming in badly out of shape. He never contended for a title again.
This aftermath matters for understanding the biggest boxing upsets. Douglas on February 11, 1990, was the best heavyweight in the world. Douglas for the rest of his career was an underachiever who could not recapture that night.
Upsets do not mean the underdog is actually better overall. They mean the underdog was better that night. Douglas proved he could beat Tyson under those specific circumstances. He did not prove he was a great champion. Those are different things, and understanding this distinction is crucial for interpreting underdog psychology.
What the Biggest Boxing Upsets Teach Us
Heavyweight boxing is particularly prone to upsets because one punch can end any fight. A fighter can be losing every round and land a single shot that changes the outcome instantly.
However, the pattern extends beyond heavyweights:
Champions get old. Ali, Holyfield, and countless others have been upset by younger fighters who simply had more left in the tank. Age in boxing is more predictable than the betting market often reflects.
Overconfidence kills. Tyson overlooking Douglas, Lewis overlooking Rahman, Joshua overlooking Ruiz. When champions stop respecting opponents, they stop preparing properly. The pattern repeats throughout boxing history.
Styles make fights. Some matchups favor underdogs in ways that records do not capture. A fighter with the wrong style for a champion might lose to lesser opponents but beat the champion. Understanding underdog win rates across sports helps contextualize why boxing produces so many shocking results.
The Betting Lesson from the Biggest Boxing Upsets
Boxing odds often reflect narrative more than probability.
A popular champion facing an unknown challenger will be heavily favored, sometimes beyond what the skill gap justifies. The public bets names, not matchups. The market adjusts, but not always enough to reflect true probability.
Heavy favorites in boxing win most of the time. However, they lose often enough that backing them at -1000 or worse is usually a losing proposition over time. The upsets in this article happened at odds ranging from 10-1 to 42-1. Those odds imply 2-9% win probability. The actual upset rate in heavyweight boxing is higher than the market suggests.
Boxing’s history is filled with invincible champions who were not invincible at all. The next upset is always closer than the odds suggest, which is why contrarian bettors continue to find value in the ring.