In the end, the Giants edged the Padres, 3-2, before a sold-out crowd as Angel Pagan doubled in the winning run in the bottom of the ninth inning in the first game of a three-game series between these two National League West rivals.
San Francisco pitcher Madison Bumgarner, who didn't figure in the decision, tied the Padres hitters in knots, striking out 10 of the final 18 hitters he faced. He allowed two runs over six innings.
Volquez, who also allowed two runs over six innings, came into Friday's game with an 0-3 record and an 11.68 ERA. But Volquez got some good mileage out of his curveball and changeup in keeping the Giants (10-7) mostly off balance.
"Volky got out of some jams," said Padres manager Bud Black. "I thought the curveball was effective against the lefties and he threw some good changes. But overall, I thought it was better than his first three starts."
Headley, playing in just his second game since coming off the disabled list Wednesday, knocked in the Padres' first run with a sacrifice fly in the first inning. He also tied the game in the sixth inning when he hit a home run to left field, his first of the season.
Headley, who led the National League in RBIs last season (115), also struck out twice and mentioned on several occasions after the game that his timing at the plate -- from each side of the plate -- was slightly amiss, the result, he said, of missing the first two weeks of the season recovering from a fractured tip of his left thumb.
"It's a matter of timing now, but it's getting better," he said. "I swung at some bad pitches. But when you're not on time, you don't see the ball as well. The good thing is that's never been an issue for me. But I would still rather swing and be aggressive rather than taking pitches."
Headley's two swings and two hits each by Chris Denorfia and Jesus Guzman were the lone highlights against Bumgarner, who actually saw his ERA rise from 1.77 to 2.05.
Volquez allowed a run in the bottom of the first inning and then another in the third inning when he walked Buster Posey with two outs and then hung a changeup to Hunter Pence, who lined a ball just over the outstretched glove of Headley and into the corner for an RBI double.
The Giants, who were 1-for-9 with runners in scoring position, threatened nearly every inning against Volquez but couldn't knock him out of the game.
The Padres (5-11) nearly turned a triple play in the sixth inning. After Brandon Belt and Gregor Blanco reached on singles, Bumgarner -- instead of bunting the runners along -- smashed a ball past Headley, who was playing in, where Everth Cabrera fielded it and tagged Belt to start a 6-4 double play. Bumgarner barely beat the throw, which was in the dirt.
Afterward, Volquez embraced the positive aspects of his start.
"I've got a better tempo between pitches and I keep the ball on the ground and throw more strikes," he said. "I thought tonight was a good sign. I threw a lot of first-pitch strikes and I had better command tonight."
In the ninth inning, Blanco slapped an opposite-field single to left field. Pinch-hitter Andres Torres tried to move him to second base with a bunt, but reliever Luke Gregerson (1-2) fielded the ball and threw a strike to second base to get the forceout.
Torres then stole second base, though he didn't stay there long. He scored easily as Pagan drilled a ball into right field to end the game.
"You want to get your job done, but I forgot about that [after the hit]," Torres said.
Santiago Casilla (2-1), the last of four pitchers, got the victory for the Giants.