MILWAUKEE -- For most of the game, it looked as though Buster Posey's first-inning home run was going to be enough.

Then the San Francisco Giants found themselves in an extra-inning marathon, finally getting a leadoff home run from backup catcher Hector Sanchez in the 14th inning for a 4-3 victory over the Milwaukee Brewers on Monday night.

"You're hoping somebody pops one," Giants manager Bruce Bochy said. "Hector is a good pick to get a pitch. That was what won the game for us tonight, a couple of home runs -- something we've been missing."

Posey hit a three-run shot in the first, but San Francisco went the next 12 innings without a run. Sanchez's second homer of the season came off reliever Juan Perez (0-1), breaking a 3-all tie in a game in which both teams struggled on offense.

"I just looked for a fastball and tried to hit it hard," Sanchez said.

Ryan Braun tied it with a two-run homer in the eighth for Milwaukee but left the game because of tightness in his right groin after grounding out to end the 10th. Braun said after the game that the injury was similar to one he had in spring training, but didn't seem overly concerned.

"It's not as bad as it was then, so it's not too serious," Braun said.

It was not clear if Braun would be able to play Tuesday night.

Santiago Casilla (1-2) pitched the final two innings for the win. He allowed a single to Taylor Green with two outs in the 14th but got Corey Hart to fly out to end the game.

The Brewers had a chance to win in the 12th when Hart walked with two outs. The Giants brought in reliever Javier Lopez, who walked Norichika Aoki. That brought up Nyjer Morgan, who grounded out to end the inning.

Madison Bumgarner gave up three runs and five hits in 7 2-3 innings for the Giants, with a season-high 10 strikeouts. Coming in, Bumgarner had allowed only four runs in four career outings against Milwaukee.

"He's good, man," Braun said. "He's been one of the best pitchers, I think, in the National League since he's been in the big leagues."

Bochy was impressed with everything he saw from his pitchers, beginning with Bumgarner.

"He threw the ball great," Bochy said. "The `pen stepped up. When you're on the road, you need that. You need it all the time, but you're living on the edge when it's a tie ballgame and you're on the road. Those guys really pitched great. All of them."

Brewers manager Ron Roenicke started Hart at first base, a move the team thought about making in the offseason before Hart hurt his knee and missed most of spring training.

Milwaukee starter Randy Wolf gave up five hits and three runs in seven innings, with three walks and four strikeouts.

Wolf labored early on, throwing 70 pitches in the first three innings. But he settled down after that, allowing only a single in the next four innings.

Wolf was coming off a four-inning outing in a May 16 loss at Houston. He gave up seven runs in that game, six earned.

The left-hander issued back-to-back walks with one out in the first and Posey made him pay for it by pounding a 2-1 pitch to left for his fifth homer and a 3-0 lead.

The Brewers loaded the bases with one out in the second, but Bumgarner got Cesar Izturis to ground into a double play.

Bumgarner cruised through the next three innings, allowing only a single, and then got a pair of groundouts to start the sixth before Braun reached on an infield hit. Aramis Ramirez doubled to right field, scoring Braun and cutting the lead to 3-1.

Melky Cabrera hit a one-out triple off Brewers reliever Francisco Rodriguez in the seventh, and Rodriguez walked Posey. Brett Pill hit a grounder to third, and Ramirez threw out Cabrera at the plate. Rodriguez then struck out Joaquin Arias to end the inning.

Aoki reached in the eighth on a fielding error by shortstop Brandon Crawford -- a fairly routine play that could have ended the inning -- bringing up Braun with two outs. Braun smacked a pitch from Bumgarner to left, tying the game.

"He was locked in at that time," Bochy said. "I have all the confidence in the world in him. I feel bad for him because he pitched a great game, but he did his job."

Notes

• Roenicke rested catcher Jonathan Lucroy even though he had two homers and seven RBIs in Sunday's victory over Minnesota. George Kottaras typically catches when Wolf starts. Lucroy pinch-hit in the ninth and flied out to end the inning.
• Giants RHP Matt Cain (3-2, 2.67 ERA) faces RHP Shaun Marcum (2-2, 3.31) in the second game of the series Tuesday.
• Attendance was 31,644.