MILWAUKEE -- Here's how good Buster Posey was Wednesday night:

The Giants hit three first-inning home runs en route to a season-high run total. Tim Lincecum sustained his Cy Young Award-winning form for seven innings. Either feat normally would suffice as the theme of the evening.

But not with the 23-year-old Posey extending the boundaries of his considerable promise so quickly, only 41 games into his Major League career.

Posey established a slew of personal bests with six RBIs, a 4-for-4 effort and two homers, including his first Major League grand slam, as the Giants routed the Milwaukee Brewers, 15-2.

After losing three of four games at Colorado, the Giants have won three in a row here as they approach Thursday's series finale and a flight to Washington for the final stop of their longest trip of the season. They remain in fourth place in the National League West but trail division-leading San Diego by only five games.

Numerous Giants contributed to sustaining the club's momentum at Miller Park, where hitters customarily thrive. Every starter hit safely and scored at least once. San Francisco's four homers represented another season high.

In the city where Willie Mays hit four home runs on April 30, 1961, the Giants wrote more hitting history.

They clobbered three first-inning homers for the first time since Aug. 22, 1999, when Barry Bonds, Jeff Kent and Ellis Burks went deep consecutively at Milwaukee County Stadium. It marked the first time San Francisco has amassed three homers in any inning since the fifth on May 7, 2007, against the Mets at AT&T Park, when Bengie Molina homered twice and Rich Aurilia added another.

Then there was Posey, San Francisco's precocious No. 1 selection (fifth overall) from the 2008 First-Year Player Draft. He became the first Giants rookie to drive in six runs in a game since Rick Parker did so on June 8, 1990, in San Francisco's 23-8 triumph at Atlanta.

The last Giant to record six RBIs in a game was none other than Barry Lamar Bonds on July 19, 2007, at Chicago.

"He's probably the best hitter of all time," Posey said. "To be even mentioned in the same [sentence] is surreal."

The Giants scored four runs in the first inning, seven in the fourth and four in the sixth. Posey contributed to each uprising.

In the first inning, Posey followed homers by Andres Torres and Aubrey Huff with a two-run long ball to left field off Brewers starter Chris Narveson (7-6).

Freddy Sanchez lined a bases-loaded triple with one out in the fourth before Narveson walked Huff and Pat Burrell. That loaded the bases and set up Posey's slam, an opposite-field drive to right off reliever Chris Capuano.

Posey's one-out infield single ignited the Giants in the sixth, which was highlighted by Torres' two-run double.

"He just feels plugged in, pretty much," Lincecum said of Posey, who's 12-for-24 with four home runs, eight runs scored and nine RBIs on this trip.

Last Thursday's finalizing of the Bengie Molina trade has relieved Posey of the daily distraction of checking the lineup card. He has felt much more comfortable as a result.

"It's nice to know that I'm going to be in there," Posey said. "My role's changed a little bit. I'm counted on a little bit more now. I'm not saying that before I didn't try to do my best. I'm giving everything I've got each game."

Even the most rabid of Giants fans would admit that this game was an aberration, given the club's typically modest offense.

"We're not a team that has many games like this," manager Bruce Bochy said in an understatement.

What wasn't an aberration -- yet still stood out as a welcome sight for the Giants -- was Lincecum's performance, which followed two consecutive losses in which he allowed eight runs in nine innings.

Lincecum sounded self-critical last Sunday after being named to the NL All-Star team, implying that he wasn't fully deserving of the honor. He had nothing to complain about this time as he surrendered four hits, including Rickie Weeks' third-inning leadoff home run, in seven innings. Lincecum struck out 10, the fifth time this season he has reached double digits and 24th in his career.

"I feel like I'm gaining a little more strength," said Lincecum (9-4). "Things are a little bit more alive. My pitches are doing what I want them to. I was able to feel on track tonight."

Naturally, Lincecum appreciated San Francisco's prodigious offense.

"That gave me a lot of leeway to relax," he said. "It's fun to watch our lineup blow up like they did tonight. We came in ready."