Pablo Sandoval homered to back Madison Bumgarner's fourth straight victory, and the San Francisco Giants beat the Padres 4-1 on Sunday to deny San Diego its first series win of the season.

Joaquin Arias added a two-run triple in the sixth inning to turn a one-run lead into 4-1.

The Giants wasted no time giving Bumgarner (4-1) a lead against Clayton Richard (1-3), a day after Anthony Bass retired the first 17 San Francisco batters before pitcher Tim Lincecum broke up the no-hit bid with an infield single with two outs in the sixth.

Bumgarner struck out a season-best six in 7 2-3 innings for his team-leading fourth victory, and he has won four straight starts since losing his season debut at Arizona. He owns a 1.61 ERA during the winning streak. Bumgarner allowed six hits and walked one.

Angel Pagan led off the first with a single, then Richard threw wildly past first on a pickoff attempt for a two-base error as the ball went to the visiting bullpen. Melky Cabrera followed with a sacrifice fly before Sandoval connected for his fourth home run after his season-opening 20-game hitting streak ended in Saturday night's 2-1 win.

The Padres scored in the fifth on Chris Denorfia's double that was misread in center field by Pagan, who took a step in before having to backpedal for a ball that traveled further than he anticipated. That scored Jason Bartlett, who got aboard on a leadoff single.

Bumgarner, who earlier this month received a $35.56 million, six-year contract that runs through 2017, struck out 13 San Diego batters in his last start against the Padres on Sept. 5, 2011. He had them guessing again this time.

The 22-year-old left-hander — second-youngest on the team behind rookie catcher Hector Sanchez — has held opponents to two or fewer runs in his last nine starts at AT&T Park. Bumgarner also has won 13 of his last 18 decisions since July 14, 2011.

Sergio Romo retired one batter in the eighth and Santiago Casilla allowed a two-out walk to Cameron Maybin in the ninth but finished for his fourth save in four chances.

Brett Pill singled and doubled off Richard, who lost his third straight start. He gave up four runs and eight hits in seven innings.

When Posey drew a walk in the sixth, it ended a stretch of 26 innings for Richard, and 104 batters faced, without allowing a free pass since Wilson Ramos walked on Thursday. According to STATS LLC, it was the team's longest such streak since San Diego went 29 innings without a walk from May 12-15, 2007.

The lefty had allowed three or fewer earned runs in his previous seven starts against the Giants dating to April 19, 2010.

Pagan extended his career-high hitting streak to 14 games in the first, then Sandoval sent an 0-1 pitch into the left-field bleachers two batters later.

Cabrera has reached base safely via a hit or walk in 21 of his first 22 games.

San Diego has lost six series and split a four-gamer with the Phillies so far this season.

NOTES: Posey made his fourth start at 1B, with Sanchez catching. ... Brandon Belt wasn't in the lineup after hitting a go-ahead, two-run double Saturday night, but manager Bruce Bochy said it was a decision based on the lefty starter. ... Orlando Hudson had the day off after going 0 for 4 on Saturday to have his 10-game hitting streak snapped — longest by a Padres player in 2012. Andy Parrino started at 2B in his place. ... Padres RHP Tim Stauffer, who began the season on the 15-day disabled list with a strained elbow, began a rehab assignment with Class-A Lake Elsinore and pitched 3 2-3 innings. He allowed six hits, two earned runs, struck out seven and didn't have a walk. ... Richard's final 2011 start came vs. San Francisco before he had season-ending left shoulder surgery.