The bout was originally scheduled as a lightweight bout, but Chiesa failed to make the 156-pound limit.
Chiesa, winner of three of his last four, fights Pettis, a former UFC champion who has alternated wins and losses in his past five outings, on the main card.
Check out the UFC 226 live blog below.
Round 1: Referee Herb Dean the third man in the cage. Chiesa catches a kick from Pettis early and takes him down against the fence. He’s sitting in half guard and throwing punches and elbows down at Pettis. The former lightweight champ avoids an arm-triangle, but he is eating ground-and-pound. However, he slickly slips out from under Chiesa and hunts for back control. Chiesa using a kimura to keep Pettis from taking control. He nearly gets a throw, but Pettis blocks it and they separate. Pettis clinches and pushes Chiesa against the fence, but Chiesa quickly reverses positions. Chiesa throws a few short punches before ducking in for a takedown, he gets it. Pettis throwing up his legs in defense, but Chiesa stacks him up and settles into full guard. Pettis throws a kick off of his back, then gets back up. Body kicks from distance score for Pettis. Pettis lands a leg kick and Chiesa goes after him with straight punches, but Pettis is maintaining the range. Right hand lands over the top for Pettis. Pettis catches a kick and trips Chiesa to the mat. A left hand at the buzzer by Pettis puts Chiesa down. Unclear if it was a knockdown or a slip, very close round.
MMA Fighting scores the round 10-9, Pettis.
Round 2: They exchange body kicks, then Pettis unloads with a straight right and Chiesa looks hurt. Flying knee by Pettis, Chiesa throws a kick simultaneously and they fall together. Pettis jumps in for a guillotine, but Chiesa reverses position and ends up on top in Pettis’s guard. Pettis throws up a triangle and it is in deep. He transitions to a triangle armbar and Chiesa taps!
Official result: Anthony Pettis def. Michael Chiesa via submission (triangle armbar) at :52 of Round 2