Mike Trout delivered the tying single and Shohei Ohtani scored the go-ahead run on Albert Pujols' groundout in the eighth inning, leading Los Angeles' rally to a 4-3 victory over the Chicago White Sox on Thursday night.
Max Stassi homered and Justin Upton had an RBI single in the Angels' first opening day at home since 2016.
Fletcher opened the eighth by beating out an infield single off Bummer's glove. Second baseman Nick Madrigal then made a throwing error on a hard-hit grounder from Ohtani, and Fletcher took third on a passed ball before Trout smacked a single to left.
Upton drew an 11-pitch walk to load the bases for Pujols, whose high-bouncing groundout easily scored Ohtani. Pujols' RBI was the 16th of his career on opening day, the most among active players.
Mike Mayers (1-0) pitched the eighth, and Raisel Iglesias needed just eight pitches in the ninth to earn the save in his Angels debut.
Adam Eaton hit a tiebreaking, two-run homer in his first game back with the White Sox.
Lucas Giolito retired the Angels' first 11 batters and pitched two-hit ball into the sixth inning for Chicago. The Southern California native baffled the Angels' lineup his first time through, striking out six of nine largely with his changeup.
Giolito left with a 3-2 lead, but the Angels jumped on Bummer and kept new closer Liam Hendriks out of the game.
Dylan Bundy yielded six hits and three runs with six strikeouts over six innings in his first opening day start for the Angels.