Upsets are an essential part of mixed martial arts. Here are 20 of the biggest in the history of the sport.

Knockouts. Submissions. Three-round wars.

All of these are exciting aspects of mixed martial arts, but perhaps the most exciting is the upset.

When two fighters enter the cage, there will likely be a favorite and an underdog. Like the names suggest, the favorite is who is expected to win, and the underdog is who is expected to lose. Most of the time, the favorite does exactly what fans and pundits alike predict, which is defeating their opponent in a method common to their fighting style. However, this isn’t always the case.

There are times where the underdog bests the favorite, resulting in the upset victory that leaves everyone stunned.

Now, there have been plenty of upsets to occur since the beginning of the sport, but there are a select few that are of historical significance. These are the upsets that truly helped shape the landscape of the sport we know and love today.

As usual, there are some factors taken into consideration when selecting these entries. For this list, we looked at the overall significance and the background story of the fight (ex. how each fighter made it to the fight or how they were expected to fare).

Because a list like this has been made numerous times before, there will be some entries you may have already seen or heard of. So yes, get ready to see Matt Serra vs. Georges St-Pierre 1! However, there will be an inclusion of more recent upsets, so don’t fret just yet.

Now that we’ve covered all bases, here are 20 of the biggest upsets in MMA history.

20. Will Brooks vs. Michael Chandler 1

Three men hold wins over Michael Chandler, who is arguably the most successful lightweight champion in Bellator MMA history.

One of those men, former Bellator and UFC fighter Will Brooks, took on Chandler for the first time in 2014 at Bellator 120. Brooks got the fight against Chandler after a shakeup in the fight plans of the former champion, Eddie Alvarez, who was scheduled to meet Chandler for their third and final fight.

Out due to a concussion, Alvarez was unable to set a timetable for a return, so an interim lightweight title was created, and Brooks and Chandler were the two men fighting for it.

Although he was fresh off winning a lightweight tournament, Brooks was not given a fair chance by many. Not only was he taking on someone as dominant as Chandler on short-notice, but Brooks was seen as somewhat of a second-rate version of his opponent.

Brooks and Chandler possess similar fighting styles, but the latter was better in all aspects. This meant most saw the fight an easy one for Chandler, who would get back on track and face Alvarez mentioned above to conclude their exciting trilogy.

But Brooks had other plans.

The fight began, and Chandler immediately moved to take the fight to the ground. As he came forward, Chandler kept the pressure high on Brooks, who was trying to find a way off his back. The two were even in the striking department, so it was the wrestling and groundwork of Chandler that saw him win the first two rounds.

Things started to change in the third, however.

Brooks started to find his rhythm and was able to get Chandler down. For a moment, Brooks appeared to be on his way to finishing Chandler when he wound up in mount and unloaded some heavy shots. In the championship rounds, Brooks maintained the same gameplan, and the fight would be tied going into the fifth.

A more aggressive Chandler came in and nearly got a finish over Brooks in the final minute, but the fight ultimately went to the judges. For those who watched, the fight should have been scored 3-2 in favor of Chandler. However, it wasn’t.

Brooks was announced the winner by split decision, upsetting the former champion. Brooks went from being a 10-1 underdog according to oddsmakers to the new interim lightweight champion in Bellator, shaking up the division once ruled by Chandler and Alvarez.