CHICAGO -- Darwin Barney is having himself quite a September.
Barney spoiled Chris Carpenter's season debut with a two-run, tying homer with two outs in the ninth inning, and David DeJesus smacked a game-winning single in the 11th to lift the Chicago Cubs over the playoff-hopeful St. Louis Cardinals 5-4 on Friday.
DeJesus' winning hit to right field on an 0-2 pitch from Joe Kelly (5-6) scored pinch-runner Brett Jackson.
Alberto Cabrera (1-1) struck out two in a perfect 11th to earn his first career victory.
The Cardinals entered Friday with a 2 1/2-game lead over the Milwaukee Brewers for the second wild card spot in the NL.
Carpenter threw five effective innings and was in line for the win until Barney sent a 1-2 pitch from Fernando Salas into the left-field bleachers.
"I'm just trying to get (Anthony) Rizzo up," Barney said. "Fortunately, he threw me another fastball and I got to it. I was worried about the wind, that the wind was going to knock it down, but it went."
Regular Cardinals closer Jason Motte wasn't used because he had pitched on three consecutive days and four of the previous five.
Barney has 25 hits in September, matching his highest output of any month this season, with eight games to play. The 26-year-old Barney is hitting .352 this month.
"I feel like there's some times where I've gone through periods of adjustments and I'm not really helping out the offense that much," Barney said. "It's one of those things where we're working on finding an approach I can stick with and take into the offseason and work on it, and hopefully come in and stick with one thing next year."
Carpenter threw 77 pitches in his debut, while a light rain fell throughout. The 37-year-old Carpenter allowed two runs and five hits. He struck out two and walked one.
"My stuff wasn't as sharp as I'd like, and it wasn't as sharp as it's been in the simulated games," Carpenter said. "It was fun to get back out there. Hopefully my stuff will get better and sharper as I get out there more often.
"This is something to build off."
Carpenter went 4-0 during the postseason last year, but he hadn't pitched since winning Game 7 of the World Series against the Texas Rangers. He had surgery July 19 to relieve a nerve ailment that caused numbness up and down the right side of his body.
Adding his experienced arm to the rotation boosts the Cardinals' playoff push. The Brewers opened a series Friday night against the Washington Nationals, who clinched a playoff berth on Thursday.
"Good to have him back out there, and obviously he did exactly what we thought he'd do," Cardinals manager Mike Matheny said. "He competed and made some good pitches and gave us a chance to win."
Carpenter held the Cubs scoreless through the first two innings, allowing three baserunners, but the aggressive Chicago hitters jumped on him in a two-run third.
DeJesus led off the inning with a triple, and Barney followed with an RBI single. Two batters later, Alfonso Soriano doubled to the left field corner to tie it 2-2.
Carpenter retired eight of the last nine batters he faced after Soriano's double.
"I'm sure Carpenter will tell you it wasn't his best stuff," Cubs manager Dale Sveum said. "I've obviously seen him with much better stuff and sharpness to everything. I think he got away with a lot of things."
St. Louis regained the lead in the fourth on a botched squeeze play. Pete Kozma led off with a triple, and was credited with a steal of home when catcher Welington Castillo was unable to handle a high-and-tight pitch that Daniel Descalso offered at but couldn't lay down.
It was the Cardinals' first straight steal of home since Kerry Robinson in 2002.
Yadier Molina's two-out single put St. Louis on the board in the first inning, and Allen Craig added a sacrifice fly in the third. Matt Holliday reached base four times for the Cardinals.
Descalso gave the Cardinals a 4-2 lead when his double in the eighth inning scored Matt Carpenter.
Cubs starter Chris Volstad allowed three runs and six hits in five innings. He also walked three.
Notes: Soriano matched his career high with 104 RBIs, set in 2005 with Texas. ... The Cardinals sent LHP John Gaub outright to Memphis of the PCL to make room on the 40-man roster for Carpenter, who was activated from the 60-day disabled list. ... St. Louis' Adam Wainwright (13-13, 3.97 ERA) will face Chicago's Travis Wood (6-12, 4.25) on Saturday afternoon.