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MILWAUKEE -- That slashing swing and those 450-foot drives in batting practice tell Brewers interim manager Dale Sveum that Ryan Braun's ribs can't be bothering him that much.

Braun tells a slightly different story, but the slugger isn't using a lingering injury to his rib cage muscles as an excuse for an extended September slump. And after hitting a 10th-inning grand slam to beat Pittsburgh 5-1 Thursday night and keep the Brewers tied atop the NL wild-card race, he might not need to.

"This is the most frustrating thing I've ever been through as a baseball player," Braun said. "I'd never make an excuse to try to justify my performance but just physically, I've been unable to do what I've been used to doing."

Until the Brewers needed it most.

Milwaukee went into the 10th tied 1-1 and their fellow wild-card contenders, the New York Mets, having already had beaten the Chicago Cubs. The Brewers loaded the bases with two out to bring up Braun, who was 0-for-4 in the game and hitting just above .200 in September.

Braun clobbered a 2-2 pitch from reliever Jesse Chavez (0-1) deep to left field, holding up his bat and hollering at the Brewers' dugout as he began to circle the bases -- celebrating the first grand slam of his career and the Brewers' first grand slam this year as a team.

"There's no better feeling in the world than a walk-off home run -- especially based on the situation that we're in," Braun said.

Sveum attributed Braun's struggles to the pressure of a playoff race more than the injury.

"Sometimes, you've got to realize that a young man like that's never gone through any adversity in his life as an athlete," Sveum said. "That guy hit in little league, he hit in high school, he hit in college, he hit in pro ball, he hit in the big leagues. And then you're thrown into the spot and sometimes, people struggle."

Mitch Stetter (3-1) earned the victory after pitching out of a jam in the 10th.

Despite their slides in September, Braun and the Brewers have three games left against the Chicago Cubs with a playoff spot on the line.

And if they do make it, they might have an unexpected ace up their sleeve: pitcher Yovani Gallardo.

Making his first start since tearing a knee ligament May 1, Gallardo pitched only four innings but made them count. The Brewers' promising 22-year-old right-hander struck out seven while giving up a run and three hits.

"It's great," Gallardo said. "I spent four months watching this team go at it every day. And it hasn't changed. They still go out there, play hard every day, and they're going to find a way to get it done."

Gallardo cruised through the first three innings as Milwaukee took a 1-0 lead on an RBI double by Bill Hall, then appeared to run out of gas in the fourth, giving up a one-out homer to Steve Pearce that tied the game.

"I am sure he did a lot of work to get where he's at," Pearce said. "Kudos to him. Good job. He looked great out there."

Expected to be the Brewers' No. 2 starter behind Ben Sheets this season, Gallardo made only three starts before tearing a ligament in his right knee while trying to hurdle a baserunner against the Cubs on May 1.

Gallardo also had arthroscopic surgery on his left knee just before spring training, but said he didn't have any concerns about returning so quickly.

"They wouldn't be throwing me out there to pitch if everything wasn't the way it's supposed to be," he said.

Gallardo's return trumped a strong outing by Pirates starter Zach Duke, who held the Brewers to a run and seven hits in seven innings.

"He threw the ball really well," Pirates manager John Russell said. "It's a big reason I sent him back out for the extra inning. It was a 1-1 game, and I really was trying to get him a win there."

Pittsburgh threatened to take the lead in the ninth, but reliever Salomon Torres got pinch hitter Doug Mientkiewicz to fly out with runners at first and second.

Game notes

Pirates OF Brandon Moss will have left knee surgery next Friday that is expected to keep him out until early next spring, general manager Neal Huntington said. The procedure will address a lack of cartilage in the knee, which is causing two bones to rub together. "This is a relatively minor injury," Huntington said. "We're expecting a full recovery." ... After a bullpen session, Brewers RHP Ben Sheets said his ability to start against the Cubs on Saturday is "up in the air." ... Brewers RHP Eric Gagne bought 5,000 unsold tickets to Thursday's game and gave them away on the Brewers' Web site. They were gone in 20 minutes. ... Pirates LF Nyjer Morgan left the game with a mild left hamstring strain in the first inning.