Angel Pagan led off the first inning with a homer, Buster Posey connected two batters later, and Yusmeiro Petit went six innings in a spot start replacing injured Matt Cain and the Giants beat the San Diego Padres 6-0 on Tuesday night.
Cain was scratched after cutting the tip of his right index finger. Manager Bruce Bochy said before the game that Cain was in the clubhouse kitchen and had a knife in his hand when the utensil dropped. Cain tried to catch it and cut his finger about a half-inch. He is expected to make his next start.
Petit (2-1) didn't allow a hit until Everth Cabrera's leadoff single in the fourth.
Hector Sanchez, starting at catcher with Posey at first base, hit a two-run single and a sacrifice fly.
Petit allowed three hits with four strikeouts and no walks.
It was his first start not allowing a run since he tossed a 1-hitter last Sept. 6 at home against Arizona. He lowered his ERA from 3.68 to 2.61.
Jean Machi pitched two innings and Santiago Casilla finished the 2-hour, 28-minute, three-hitter, San Francisco's second shutout this season. The Padres were blanked for the fourth time.
The Giants said Cain wouldn't require stitches on his pitching hand.
"It's on the forefinger about half an inch, but it's in a bad spot there," Bochy said. "It'll be closed up in a couple days and he should be fine."
Cain, who pitched a perfect game two years ago at AT&T Park, will finish winless in April. He is 0-3 with a 4.35 ERA in five starts.
Pagan sent a 1-1 pitch from Eric Stults (1-3) just inside the left-field foul pole for his second homer, then Posey hit his sixth one out later.
It was Pagan's seventh career leadoff homer and first since May 1, 2013, at Arizona.
The Giants hit two homers in the first inning at AT&T Park for the first time since Fred Lewis and Bengie Molina did so on July 22, 2008, against Washington.
San Diego's Yamani Grandal made his first career start at first base as manager Bud Black gave struggling Yonder Alonso a break.
Stults was done after 2 2-3 innings, allowing five runs and seven hits.
San Diego will try to win Wednesday's rubber game for their first road series victory this year and snap a nine-series winless streak at AT&T Park dating to a three-game series here from Oct. 1-3, 2010, one that sealed the Giants' division title on the way to the city's first World Series championship.
NOTES: Home run king Barry Bonds made an appearance at the ballpark. ... Padres OF Seth Smith was available off the bench but missed his fourth straight start as he nurses a strained groin sustained Thursday night against the Nationals. He could start Wednesday night's series finale. ... Giants RHP Tim Hudson tries for his fourth victory, facing LHP Robbie Erlin (1-3). ... The Giants improved to 11-1 when scoring first. ... It was an usually warm 76 degrees at first pitch. ... Giants LF Michael Morse and RHP Ryan Vogelsong had their guitars autographed by Metallica.