What could be boxing's craziest fight is now a certainty. One of the best boxers ever to have lived, the incredible 49-0 Floyd 'Money' Mayweather Junior is coming out of retirement to fight Connor McGregor, a mixed martial artist who, despite excelling in his weight classes as a UFC fighter, has never fought a professional boxing match in his career. Even though he is entering the match as a complete underdog, many gamblers won't be able to help themselves. If you are eager to learn more about the history of sports greatest underdogs then read this fantastic blog post all about winning against all odds.

If McGregor does manage to win the bout, it wouldn't be the first time that a complete underdog has gone on to defy the odds and demolish the favourite, so we're taking a look at the top 5 upsets in boxing history to get in the mood for what could be a shock result (if Mayweather fights blindfolded...)

  1. Manny Pacquiao v Oscar de la Hoya

Although not that shocking today, Pacquiao went into this fight the underdog, with de la Hoya tipped to win this 'easy' match and possibly face Floyd Mayweather. The 'Golden Boy' was absolutely dominated by Pacquiao however and never fought again, a sensible decision after the hiding that the Filipino delivered. Pacquiao earned the Mayweather fight, losing over 12 rounds to a unanimous decision.

  1. Tyson Fury v Wladimir Klitschko

The two giants met in the ring in Dusseldorf in 2015 after some mud-slinging, mostly around how boring Klitschko is. The fight went 12 long rounds, becoming more of a game of chess than a fight, but the judges decided that Fury was the better boxer, awarding him the decision even though he was docked a point for a punch to the back of the head. The match saw the end of Klitschko's 10 year reign and Fury performing some awkward karaoke to celebrate.

  1. Muhammad Ali v Leon Spinks, 1978

Although Ali was coming off the back of three massive fights including the Thrilla in Manilla against Joe Frazier and bouts against Ernie Shavers and Ken Norton that were won on points, no one expected the young Olympic heavyweight champion Spinks to come out and beat the greatest boxer of all time. But that he did, managing to not only avoid tiring himself out chasing Ali around the ring looking for punches, but avoided Ali's brilliant tactics to take the belt. They met again in the ring, where Ali took back the belt from the only man who ever managed to win it off him in the ring.

  1. Muhammad Ali v George Foreman

Zaire had the completely opposite effects on each boxer, with Ali lapping up the limelight and finding his feet in the Central African nation ahead of the 'Rumble in the Jungle'. Foreman on the other hand seemed to hate every minute of it, refusing to leave his training compound and delaying the match 7 weeks thanks to a cut eye sustained in sparring. Ali had only narrowly won his last 2 fights and Foreman was expected to dominate, being the heavier boxer with more power. Everything was thrown out of the window however, when Ali found the canvass to be quite soft underfoot. He realised he would run out of steam with the 'float like a butterfly' tactic, so a new strategy was formulated on the spot – the rope a dope. Against advice, Ali let Foreman come at him, taking a battering whilst looking for that one magic punch. When it looked like Foreman was gaining the upper hand, Ali bided his time and came back with a stunning punch that would leave Foreman unable to get up.

  1. Mike Tyson v Buster Douglas, 1990

Iron Mike was at the top of his game, undisputed, undefeated and demolishing very good boxers, sometimes with ease. He was being hailed as one of the greatest of all time, but a 42-1 long shot in Columbusite Buster Douglas, knocked Tyson from his Heavyweight Championship pedestal. Although Tyson was his usual terrifying self, putting Douglas on the canvas in the 8th, he took a massive uppercut followed by jabs in the 9th whilst probing for a match finisher. Tyson tried his best to get up, looking for his mouthguard in the process, but the count out came and Douglas walked away with the belt.