SAN FRANCISCO -- To many Giants fans, Edgar Renteria's biggest flaw was not being Manny Ramirez. But Renteria impersonated the Dodgers slugger nicely Tuesday.

Renteria's fourth-inning grand slam off San Diego ace Jake Peavy was the defining moment in an eventful game at AT&T Park, where the Giants subdued the Padres, 8-3.

The paid crowd of 39,314, swelled by approximately 11,000 extra patrons on Filipino Heritage Night, saw more than Renteria's five-RBI outburst, which tied a career high.

Filipino hero Manny Pacquiao, acknowledged as the world's best boxer, threw the ceremonial first pitch. Catcher Bengie Molina barely missed executing the rare feat of tagging out two runners at home plate on a single play. And Matt Cain ended a personal 10-start winless streak against the Padres.

But Renteria did the most to reverse his team's fortunes against the Padres, who swept the Giants in three games at San Diego two weekends ago.

Renteria entered the game batting .200 with a .250 slugging percentage and one RBI, which must have made numerous skeptics feel smug. The two-year, $18.5 million deal the Giants gave him last December was widely criticized as one of the most ill-advised free-agent signings of the offseason, if not the worst.

Giants backers kept clamoring for Ramirez until the minute he rejoined the Dodgers. Ultimately, adding Renteria was the only significant move San Francisco made to upgrade the offense that ranked last in the Major Leagues in home runs and next-to-last in the National League in scoring a year ago.

The Giants believed that Renteria, a career .290 hitter entering this year, remained capable of contributing offensively despite his ordinary 2008 season with Detroit. He hit .270, a 62-point drop from 2007. But he has looked more competent lately, batting .467 (7-for-15) during a five-game hitting streak that has raised his average from .138 to .250.

"I've been feeling much better. I'm more patient," Renteria said.

He turned aggressive during his fourth-inning plate appearance. The Giants, winners of three of their last four games, filled the bases with one out on Molina's single, Pablo Sandoval's infield single and Travis Ishikawa's walk. Up came Renteria, who deposited Peavy's first-pitch slider halfway up the left-field pavilion, erasing San Diego's 2-1 lead.

The grand slam was not only the seventh of Renteria's career, but it was also the first off Peavy (2-2) in his eight Major League seasons. Maybe this was no surprise, given Renteria's .455 lifetime average (10-for-22) off Peavy.

"He always competes," Renteria said. "I have a lot of respect for him. Today I got lucky."

A 14-year veteran, Renteria has inspired similar respect among his new teammates for remaining unflappable while his performance has fluctuated, prompting manager Bruce Bochy to drop him from second to eighth in the batting order.

"He never changes his attitude," Ishikawa said. "He goes out there professionally."

With one swing, Renteria gave the run-starved Cain more support than he usually receives. Cain expressed his appreciation after Renteria crossed home plate by giving the shortstop a congratulatory slap on the fanny.

Asked after the game if Renteria felt like his best buddy right then and there, Cain didn't hesitate to respond.

"He is," Cain said. "I don't think you can say much more than that."

Cain (2-0) sustained the Giants' momentum by blanking San Diego in his final two innings after Renteria's slam. The right-hander, who was 0-5 despite compiling a 3.59 ERA during his drought against the Padres, improved to 28-6 lifetime while receiving three or more runs. Cain allowed two runs and nine hits in six innings while walking none and striking out five.

The key figure in Cain's pitching line, of course, was his walkless total, reflecting his growing maturity as a pitcher.

"It's one of those things where I try not to think about it," Cain said. "... You just worry about throwing strikes early [in the count], try to put pressure on them and get them in that swing mode."

Refraining from swing mode helped Ishikawa win the evening's unofficial "inside baseball" award. He fell behind Peavy 0-2 in the fourth inning yet still drew the walk that set up Renteria's homer.

"He made a great adjustment by not chasing those pitches," Bochy said of Ishikawa, who also stroked a two-run, eighth-inning single.

Molina would have made the biggest adjustment of all had he managed to tag both Adrian Gonzalez and Chase Headley on Kevin Kouzmanoff's fourth-inning drive off the right-field wall. But he missed the sliding Gonzalez with his swipe of the glove before tagging Headley on the right foot as he leaped over him. Molina and Bochy argued passionately for a double play, but later realized that plate umpire Jeff Nelson was correct.

"There was a lot of action going on and he got both calls right," Bochy said.

There was a lot going on, period.