The Cardinals took two of three from the Cubs. Chicago has lost three of four overall.
Carpenter hit a two-run single in the second inning and added a sacrifice fly in the fourth that put St. Louis ahead to stay at 4-3.
Wacha (2-0) allowed three runs and five hits in 6 1-3 innings. He gave up a two-run homer to Anthony Rizzo on his 16th pitch of the game.
Wacha struck out eight and walked one.
Edwin Jackson (0-1) allowed four runs and eight hits in six innings. He struck out five and walked three in a grueling 114-pitch effort.
The game was delayed 46 minutes because of rain in the bottom of the third inning.
Jhonny Peralta highlighted a two-run eighth with an RBI double.
Rizzo's second homer of the season put the Cubs ahead. After Carpenter singled in the second, he stole second and scored on Kolten Wong's single.
Siegrist retired all five batters.
NOTES: The Cubs are winless in their last nine series. Their last series win came in September when they won two of three in Cincinnati. .... St. Louis begins a 10-game road trip Monday with the first of a three-game set in Milwaukee. Lance Lynn (2-0, 6.55 ERA) takes on Matt Garza (0-1, 2.57) in the opener. ... The Cubs conclude a five-game road trip with two games against the New York Yankees. Jason Hammel (2-0, 2.63) faces Masahiro Tanaka (1-0, 3.21) in the first game on Tuesday. .... St. Louis C Yadier Molina has 11 hits in his last 22 at-bats, including two hits on Sunday.
Link to box score: St. Louis (7-5) 6, Chicago 4
Join the pre-game, in-game and post-game discussion about each contest at The Cardinal Nation message board.