Posey homered off the Miller Park scoreboard and had three RBIs as the Giants beat the Milwaukee Brewers 6-4 on Tuesday night.
It was his sixth homer of the season and second in two days. He hit a three-run homer in the top of the first inning Monday night in the Giants' 4-3, 14-inning win over the Brewers -- a game in which he caught the first 12 innings.
"That was a long game yesterday," said Posey, who was injured in a collision with Florida's Scott Cousins on May 25, 2011, ending his season. "To come back today and feel good is a good sign."
Posey is batting .500 (12-24) with six home runs and 15 RBIs in six games at Miller Park. Despite the great numbers in Milwaukee, manager Bruce Bochy said he likely would stick with his plan for Posey during the team's seven-game road trip.
That means his star catcher will be on the bench Wednesday in the final game of the series.
"His ankle's not a factor," Bochy said. "He did a nice job both behind the plate and swinging the bat. I was a little concerned today that it would be a little cranky, but it wasn't at all."
The Giants won for the eighth time in 11 games despite being outhit 11-5.
The Brewers went 2 for 13 with runners in scoring position off San Francisco starter Matt Cain (4-2) and have lost six of seven.
"It seemed like when he got in trouble, he really beared down and made some quality pitches," Posey said.
Cain pitched out of trouble, allowing four runs on 11 hits without walking a batter and striking out eight in seven innings.
"A lot of them were over the plate and bad location," Cain said. "But we were able to score some runs and keep the momentum on our side, and that was good."
Santiago Casilla pitched the ninth for his 11th save, leaving the Brewers frustrated.
"We're just waiting for something to click," Milwaukee's Nyjer Morgan said. "Don't know when. That's the most frustrating thing about it."
Milwaukee's Shaun Marcum (2-3) gave up six runs on five hits and two walks with five strikeouts in six innings. It was the first time this season the right-hander gave up more than three earned runs.
Posey's ground-rule double in the first scored Brandon Crawford to give the Giants a 1-0 lead. His two-run homer in the sixth ricocheted off the center field scoreboard and extended San Francisco's lead to 6-2.
Joaquin Arias hit his first major-league home run off Marcum in his 331st career major-league at-bat to give San Francisco a 4-0 lead in the fourth.
Ryan Braun's single in the seventh extended his hitting streak to 11 games and scored Aoki from third to pull Milwaukee within 6-4. Aramis Ramirez came up as the tying run, but Cain struck him out on his 115th and final pitch to end the Brewers' threat.
After Posey's double in the first, Angel Pagan hit a sacrifice fly to score Cabrera and give the Giants a 2-0 lead.
Milwaukee cut it to 4-2 in the bottom of the fourth when Rickie Weeks, in a 4-for-46 slump, hit a two-run double off the base of the center-field wall.
Game notes Cain has held batters to a .125 average (7-56) with runners in scoring position this year. ... The Brewers are 3-24 with runners in scoring position in the first two games of the series. ... Pagan went 0-3 with a sacrifice fly to snap his 11-game hitting streak. ... Brewers 1B Mat Gamel underwent surgery to repair his torn anterior cruciate ligament on Tuesday. ... Braun, who left Monday night's game in the 10th inning with a tight right groin, was back in the starting lineup Tuesday night. ... SF INF Aubrey Huff started at 1B, his first start since April 21. He had been on the DL due to an anxiety disorder.