SAN FRANCISCO -- Right-hander Allen Webster saved the best start of his season for his debut Saturday with the Arizona Diamondbacks.

Webster, who was called up from Triple-A Reno, allowed two runs and two hits in 5 2/3 innings in a 4-2 victory over the San Francisco Giants at AT&T Park.

Webster came into the game with a major-league career mark of 6-5 with a 6.25 ERA in 19 games for the Boston Red Sox, who traded him to Arizona in December. He went 1-2 with a 9.00 ERA in five appearances for Reno this year and was on the disabled list from April 20 to May 26 with a fatigued right shoulder.

"I've definitely had a rocky road so far," Webster said. "I'm happy to show them. Hopefully we can feed off this and do it again."

Webster held the Giants hitless for 5 1/3 innings until second baseman Joe Panik rifled a double down the right-field line after left fielder Nori Aoki walked.

Center fielder Angel Pagan brought Panik home with a sacrifice fly and catcher Buster Posey roped an RBI double to left, cutting Arizona's lead to 4-2 and ending Webster's outing.

"He did a great job," Diamondbacks manager Chip Hale said. "He had that sinkerball working, his changeup, a lot of groundballs. With this defense we have, we're always comfortable with that. That's something we liked about him when we traded for him. Now that he's feeling good ... it seems like he's throwing the ball well."

Giants right-hander Ryan Vogelsong (4-5) lasted just 3 2/3 innings, his second shortest start of the season, and lost his third straight game. He allowed four runs and six hits, walked five and struck out just one.

"I was off balance in the stretch," Vogelsong said. "I couldn't put it together. I was just awful. When I'm missing it's mechanical. I was trying to fix stuff but I was trying to fix the wrong thing. Sometimes the hard part is the diagnosis. I was falling into bad habits and wasn't able to make a pitch. I felt great in the bullpen, but sometime between then and the first inning things weren't right."

The Diamondbacks made Vogelsong pay for his lack of control.

"I think that's the sign of a good hitting ball club, a team that's looking for their pitch and doesn't swing at the pitcher's pitch," Arizona catcher Jarrod Saltalamacchia said. "That's what we did a great job of today, and that's why we got some runs on the board."

Diamondbacks relievers Andrew Chafin, Randall Delgado and Brad Ziegler combined to blank the Giants on two hits in the final 3 1/3 innings. Ziegler pitched a scoreless ninth for his eighth save.

Arizona first baseman Paul Goldschmidt and left fielder David Peralta each went 2-for-4 with an RBI and a run.

The Giants lost their seventh straight game at AT&T Park, their longest home skid since losing seven in a row from May 14 to May 31, 2008. Arizona improved to 5-1 at AT&T Park this season.

The Giants, who are without injured right fielder Hunter Pence, had only two hits in a 1-0 loss to Arizona on Friday night when right-hander Chase Anderson held them hitless for 7 1/3 innings. They've scored only 98 runs in 32 games at home compared with 160 runs in 31 road games.

"The offense right now, we're out of synch," Giants manager Bruce Bochy said. "The first five innings we looked dead. They brought up a kid and he threw well. Sure we miss a guy like Hunter, but this is a good offensive club."

Webster walked two batters in the first inning but escaped unscathed, then got a pep talk from Saltalamacchia, who caught him in Boston and the minor leagues.

"I definitely had the jitters," Webster said. "Once I came back into the dugout (Saltalamacchia) was able to settle me down and we got out there and got into a good rhythm together. We just rolled with it."

The Diamondbacks built a 3-0 first-inning lead after Vogelsong retired the first two batters he faced. V