Matt Cain (2-1) failed to walk a batter for just the sixth time in 107 career starts, underscoring a workmanlike six-inning stint that saw him leave the game with another rarity a four-run lead.

Free-agent shortstop Edgar Renteria and the Giants, for that matter shook out of a season-long slump. Renteria went 3-for-4 and tied a career high with 5 RBIs.

With his fourth-inning grand slam, Renteria accounted for as many runs as the Giants had scored in their three previous games combined and quadrupled his own RBI total for the season entering the game.

Nate Schierholtz not only got into a game for the first time in more than a week, but lined a double to left as a pinch-hitter in the eighth inning

It all added up to the Giants beating Padres ace Jake Peavy (2-2) for their fifth win in seven home games this season, including three of the past four.

The Giants finally got some bang out of their recent lineup shuffling after scoring two or fewer runs in six of the previous seven games. But the biggest contributor was a guy who last week was dropped from the No. 2 spot in the order to eighth because he wasn't even close to hitting his weight.

Renteria, who is listed at 200 pounds, was the Giants' biggest free-agent acquisition last winter. But he hadn't made a very good impression, opening the season in a 4-for-29 (.138) funk.

None of that mattered after Renteria blasted a first-pitch slider from Peavy into the left-field stands, turning a 2-1 Giants deficit into a 5-2 lead.

Renteria had begun to show signs of coming around before his first homer in a Giant uniform. He had gone 5-for-12 since moving into the No. 8 spot, including a first-inning single in the third inning. Renteria came around to score the Giants' first to run to tie the score at 1-1.

That tie was broken in a strange fourth inning that left players on both teams and many in the crowd at AT&T Park running for the replay monitors.

Cain appeared headed for trouble when he allowed successive singles to Adrian Gonzalez and Chase Headley.

Kevin Kouzmanoff then lined a drive toward right field. Gonzalez and Headley had to wait to see if the ball would be caught, and when the ball hit off the brick fa ade, both runners took off.

Headley, however, caught up to Gonzalez just as the Padres first baseman was rounding the third base bag. The duo raced toward home about two strides apart.

That's when it got interesting, because Giants first baseman Travis Ishikawa's relay throw to catcher Bengie Molina beat the Padres convoy to the plate.

Gonzalez made a nice slide to get around Molina's tag, swiping the edge of the plate wit his left toe. Then, as Molina was rolling on his back, Headley leaped over the Giants catcher.

Molina swiped Headley's foot mid-hurdle. But adding to the confusion, at the same time Gonzalez, apparently not sure if he had touched the plate or not, lunged at home and was tagged by Molina.

After a few seconds of suspense, home plate umpire ruled Gonzalez safe and Headley out on Kouzmanoff's RBI double. Molina and Manager Bruce Bochy argued, but to no avail.

Cain prevented any more damage by striking out Henry Blanco and getting Luis Rodriguez to pop out to Renteria to leave Kouzmanoff stranded at second base.

Cain certainly didn't have his best stuff, allowing nine hits and allowing at least one runner on base in every inning he worked. But he didn't walk a batter and never allowed any jams into big innings.

Although Cain had seven strikeouts, most of the Padres' rallies fizzled when they put the ball in play.

"He's become more of a complete pitcher," Bochy said before the game when asked about Cain's development this season. "He's not relying on just his fastball. His secondary pitchers are getting over and he's using them. He's grown up quite a bit as a pitcher."

Giants 8, Padres 3 ?Today: in San Francisco, 12:30 p.m. ?TV/Radio: CSN/KNBR (680)