UFC 166: Velasquez vs. dos Santos III was a mixed martial arts event held on October 19, 2013, at the Toyota Center in Houston, Texas. The main event was a UFC Heavyweight Championship bout between the current champion Cain Velasquez and top contender Junior dos Santos. The two have split their two previous encounters with Dos Santos winning the first bout via first round knockout and then Velasquez winning the rematch via unanimous decision at UFC 155.