Oakland immediately jumped on Bumgarner, who yielded five runs and seven hits in 2 2/3 innnings after missing his previous start with a strained rib cage and inflammation in his left foot.
Billy Burns opened the game by drawing a walk and scored on Jed Lowrie's ground-rule double. Jake Smolinski added an RBI double in the second inning before the A's made the score lopsided with a three-run third. Khris Davis singled home a run before scoring on Billy Butler's first homer of the spring.
Ehire Adrianza's alert baserunning led to a third-inning run that helped the Giants avert a shutout.