Mixed martial arts is one of the most unpredictable sports in the world. Anything can happen, and all it takes is one punch or a split-second mistake to completely alter or end an event. This is especially true in the UFC, where the best fighters in the world square off. Still, there have been some fighters who were never supposed to lose their bouts. Sean Strickland is a prime example of this. He was just handed the middleweight belt after surprisingly dethroning Israel Adesanya as champion at UFC 293. Adesanya was a -750 favorite to beat the challenger, yet Strickland dominated nearly the entire fight, ending Adesanya's second reign as champ. Strickland's victory will forever be remembered as one of the biggest upsets in the history of the sport. Here's more on that and the other biggest upsets in UFC history.

5. Israel Adesanya vs. Sean Strickland: UFC 293

Sean Strickland was an interesting choice to get a title shot at UFC 293. He was the fifth-ranked middleweight and only 2-2 in his last four bouts. Yet, Strickland was the man for the job because Adesanya had already defeated most of the other highly ranked middleweights. Strickland didn't disappoint, delivering one of the biggest upsets in UFC history.

The difference between this fight and many other great UFC upsets is Adesanya vs. Strickland wasn't decided because of one punch/kick or a fluke incident. Instead, Strickland just out-fought Adesanya for nearly the entire match. He won every round but the second and took the unanimous decision 49-46.

Critics claimed Strickland wasn't a powerful enough striker and lacked too much grappling to be able to beat Adesanya. So, Strickland won with defense, deflecting nearly everything that The Last Stylebender threw at him. Strickland allowed Adesanya to connect on only 34% of his significant strikes. Although Adesanya didn't look like himself, Strickland implemented a perfect game plan, which was surely part of what threw the defending champion off. The victory made Strickland the 14th middleweight champion in UFC history.

4. Conor McGregor vs. Nate Diaz: UFC 196

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The Notorious Conor McGregor had the most iconic run in UFC history. From his debut in 2013 through 2016, McGregor was on top of the world, and no one could touch him in the Octagon. That was, of course, until he took on Nate Diaz at UFC 196.

The two weren't originally supposed to square off. McGregor, the featherweight champion, was slated to face lightweight champion Rafael Dos Anjos. When Dos Anjos dropped out because of injury, Nate Diaz filled his spot in the match against McGregor only 11 days before the bout. The two fought at a catch weight of 170 pounds, making McGregor move up two weight classes from where he had won his belt only months before.

Still, there was so much hype around McGregor that he was expected to beat Diaz fairly effortlessly. McGregor's striking was unmatched in the fight game, and he looked to finish Diaz early. But Diaz is a known tough guy, and he is able to take punches better than almost anyone. While fighting at a bigger weight, McGregor gassed out earlier than expected and was submitted in the second round.

While moving up weight classes is never easy, McGregor was so skilled as a striker that his loss to Diaz came as a major surprise. McGregor evened the score at UFC 202, and the world is still awaiting a highly anticipated rubber match.

3. Ronda Rousey vs. Holly Holm: UFC 193

Ronda Rousey was the most dominant woman in UFC history during her prime. She was a massive -1400 favorite to remain unbeaten when she took on Holly Holm at UFC 193.

In 2015, Rousey was not only the face of the UFC, but she was arguably the biggest female name in all of sports. Rousey was ending fights in mere seconds, but Holly Holm was no slouch. Holm played better defense than Rousey's previous opponents, not allowing the champ to get her to the ground.

A number of southpaw punches and a deadly kick to the face gave Holm the win and dropped the jaws of UFC fans everywhere. Rousey went from dominating the sport to only fighting one more time in the UFC, a bout in which she once again lost.

2. Anderson Silva vs. Chris Weidman: UFC 162

Many people consider Anderson Silva to be the best UFC fighter of all time. He certainly had one of the best title runs ever. Silva defended his middleweight title 10 times over the course of a 2,457-day reign, the longest in UFC history for any weight class. Some people thought Silva would never lose, and he won 17 straight flights before taking on Chris Weidman at UFC 162.

Silva was a master of the knockout, and his bout against Weidman was expected to end in a familiar fashion. Instead, Weidman completely altered the trajectory of Silva's career.

UFC 162 was a prime example of why you should never underestimate your opponent nor celebrate before it's over. Silva was showboating and faking that Weidman's punches were wobbling him because he thought that he could toy around with the challenger. Instead, karma got him hard, and Weidman not only knocked out the champion in the second round, but he effectively ended Silva's dominance. Silva's loss sent him into a downward spiral, and he went on to only win one of his next eight UFC fights.

1. Georges St-Pierre vs. Matt Serra: UFC 69

The fourth edition of The Ultimate Fighter gave former UFC fighters who had been previously cut from the promotion a chance to not only return to the UFC but also get a shot at the title. Matt Serra won the show and was faced with the daunting task of taking on Georges St-Pierre, the UFC's best fighter and a man who looked unbeatable.

St-Pierre had won 13 of his first 14 UFC fights. He was not supposed to lose to a middling fighter like Matt Serra, especially for the welterweight title.

Serra knew the challenge that was ahead of him, but he maintained confidence and played his own game. Serra was aggressive and knew he had to get up and into St-Pierre to stand a chance. He aggressively threw punches that slowly withered St-Pierre away. Eventually, the challenger was able to stun St-Pierre enough to where the champion couldn't recover, completing the knockout in the first round to give the UFC their most random champion ever.