If there is anything we have learned in the short history of this sport, it's that anything can happen in a fight. No favorite is ever safe and no bet is ever truly a lock.
So many champions have lost their titles in fights that were supposed to be easy wins.
At the same time, there are a list of fighters that were figured to have no shot at the top of the sport, but are remembered forever because of one signature victory.
It is one of the reasons this sport is so great. Everything can change in the blink of an eye. Sometimes a favorite just has an off night, and sometimes a dog is just motivated enough to fight off the common logic.
Bla, bla, bla... nobody reads intros, so onto the list of the 45 greatest MMA upsets of all time.
DISCLAIMER: You will see Sergey Golyaev's win over Takanori Gomi and more noticeably Frankie Edgar's win over B.J. Penn missing from the list. The reason is because I don't believe those results were correct. Just because the judges were clueless about those fights, doesn't mean that we have to be. I do mention them though because the people that did bet on the underdogs in those fights were paid.