19. Conor McGregor suffers first loss to Nate Diaz, then wins rematch

Conor McGregor suffered his first loss in a huge upset at UFC 196 at the hands of Nate Diaz. Diaz—who was replacing Rafael dos Anjos on the card after the latter had to pull out due to injury—did what was previously thought to be impossible: taking down the Irishman. McGregor would later get his revenge in their rematch at UFC 202 in a narrow decision that is disputed to this day. — Allen Kim