SAN FRANCISCO -- Chad Gaudin continued to look more like a regular member of San Francisco's starting rotation and less like a fill-in Friday night.
Gaudin limited the Arizona Diamondbacks to three hits in seven innings and didn't allow a runner past first base as the Giants outlasted the National League West leaders, 2-0.
The Giants scored both of their runs in the first inning and moved only two men into scoring position afterward. With that kind of offense, fending off Arizona required airtight pitching, and the Giants received it from Gaudin -- again.
The right-hander improved to 4-0 with a 2.23 ERA in seven starts since leaving the bullpen to replace injured Ryan Vogelsong in the rotation. Gaudin has been especially effective in his last four outings, recording a 0.77 ERA in that span.
Giants manager Bruce Bochy was inevitably asked whether Gaudin might remain a starter, particularly when Vogelsong is reinstated from the disabled list in mid-August, as expected. Bochy delivered the only sensible response he could, under the circumstances.
"We'll cross that bridge when we come to it," Bochy said. "But he has been so consistent, it would be hard to take him out."
Gaudin, who entered this season with 314 relief appearances and 75 starts on his Major League resume, has relished his prominent role. But he indicated that he won't complain if he has to relinquish it.
"Obviously, I'd like to start," he said. "If it comes down to me going to the 'pen, and that's what's best for the team, then I'll be down there ready to go."
The 30-year-old Gaudin performs with relatively little artifice. Though he'll change speeds and locations as every pitcher should, he doesn't rely on fooling hitters. Teammate Sergio Romo described Gaudin's style as "direct," adding, "There's no gimmicks. He's just really aggressive in the strike zone. As a starter, you can see his confidence growing."
Gaudin said that his approach stems from "knowing what you want to do before you go out there. You pitch with 100 percent commitment. ... I've learned the hard way it's not how nasty your stuff is or how hard you throw. It's how you go after the hitter."
Gaudin might have delivered that advice to the Giants' bullpen after he departed. The D-backs loaded the bases with two outs in the eighth, but right-hander Santiago Casilla, making only his second appearance since undergoing right knee surgery and being sidelined for close to two months, showed the Giants what they had missed. Casilla coaxed a fielder's-choice grounder to shortstop from Paul Goldschmidt, Arizona's All-Star first baseman who has eight home runs and 28 RBIs against the Giants since 2011.
"Casilla's back!" exclaimed Romo, who followed with a perfect ninth inning for his 22nd save in 25 chances.
Bochy chuckled upon being reminded that he had said he would try to "ease" Casilla back into the setup role. "You're kind of forced to bring the guy in," said Bochy, who used three other pitchers in the eighth before summoning Casilla.
Arizona starter Ian Kennedy (3-7), who had won five decisions in a row spanning 10 starts against San Francisco, lapsed only in the first inning. Gregor Blanco drew a leadoff walk and scored on Buster Posey's double off the center-field wall. Posey moved to third base on Pablo Sandoval's groundout and scored on Hunter Pence's two-out single.
Afterward, Kennedy regained his typical mastery of the Giants. "The fastballs were better [down] by the third inning," said the right-hander, who absorbed his first loss to San Francisco since Sept. 29, 2010. "I was getting ground balls. It allowed me to work better with offspeed pitches."
The reigning World Series champion Giants, striving to climb out of fourth place in the West, improved to 28-20 against division rivals and trimmed their deficit to 5 1/2 games behind Arizona.
"We can't keep looking ahead of ourselves," Romo said. "But today was a great way to start the second half."
The Giants received a scare in the eighth inning when D-backs reliever Heath Bell stepped on the left foot of shortstop Brandon Crawford, who was striving to beat the pitcher to first base after hitting a comebacker. Crawford remained in the game. "It'll be sore for a couple of days. But it's playable," he said.
Chris Haft is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.