Tanner Roark pitched five innings to get the win in his Oakland debut, and the Athletics beat Adam Wainwright and the St. Louis Cardinals 4-2 on Sunday.
Jurickson Profar connected for his 15th homer as the A's won for the sixth time in seven games. Dustin Garneau had two hits and two RBIs after he was claimed off waivers Saturday.
St. Louis fell 1 1/2 games back of NL Central-leading Chicago, which swept Milwaukee with a 7-2 victory.
Paul DeJong homered for the Cardinals, who lost each of their four games against the A's this season.
Roark (7-7) allowed one run and four hits, struck out six and walked two. The veteran right-hander pitched out of a pair of jams in his first start since he was acquired in a trade with Cincinnati at Wednesday's deadline.
The Cardinals twice had two on and two out against Roark but failed to score each time. Marcell Ozuna struck out to end the third, and Matt Carpenter struck out swinging in the fourth.
Liam Hendriks retired three batters for his 11th save.
Garneau also came up big in his second stint with the A's after being put on waivers by the Los Angeles Angels earlier this week. He singled leading off the third, hit a go-ahead two-run double off Wainwright in the fourth and walked and scored on a wild pitch in the eighth. Garneau played 19 games with the A's in 2017.
Wainwright (7-8) struggled with his command most of the afternoon. The right-hander hit two batters, walked three and allowed three runs in 5 2/3 innings.
Carpenter was 1 for 5 with two strikeouts in his first game back off the injured list. Carpenter missed 17 games with a bruised right foot.
Profar connected in the sixth, belting a towering drive that landed midway up the staircase beyond the wall in right field.