St. Louis took two of three from the Cubs and has won four of six. Chicago has lost three of four.
Rain has figured in all three of Wacha's starts this season. He actually seemed to embrace a third-inning downpour that halted play against the Cubs for 46 minutes.
"I'm used to it," he said. "You just have to accept it and you've got to stay focused. I tried to stay loose and just keep my mind in what I needed to do."
Wacha's first start of the season was delayed before first pitch by 2 hours, 40 minutes. He endured a short 12-minute delay at the outset of his second outing.
Wacha (2-0) allowed three runs and five hits in 6 1/3 innings Sunday. He gave up a two-run homer to Anthony Rizzo on the 16th pitch of the game, but yielded just one run on three hits the rest of the way. He struck out eight and walked one.
"At the start, I was a little erratic, but I was able to settle down a little bit," he said. "I got some quick innings and some quick outs."
St. Louis manager Mike Matheny says Wacha has the mental makeup to handle lengthy or short delays.
"He's strong and he knows what to do out there," Matheny said. "He keeps a good focus. I felt like his curveball was a lot better after the delay."
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. He is tied with Yadier Molina for the team lead with nine RBI.
"It felt good to get the job done," Carpenter said. "When you get up in those situations, you just try and put a good at-bat up there and I thought I did that."
Carpenter then gave St. Louis the lead for good with a sacrifice fly to left that brought in Peter Bourjos, who began the fourth inning with a triple.
"We did the things we had to at the right times to win," Carpenter said.
Trailing 4-3, Mike Olt led off the Cubs seventh with a double off Wacha. Castillo struck out and reliever Kevin Siegrist retired Darwin Barney and Bonifacio to end the threat.
Siegrist retired all five batters he faced.
"We had some chances, just couldn't get hits at the right time," Rizzo said.
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.
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