Collmenter pitched eight strong innings but the Arizona Diamondbacks lost to the Giants 2-1 on Tuesday night.
Collmenter (10-8) allowed two runs and seven hits in eight innings.
"He was dominating," catcher Miguel Montero said. "He made good pitches. Even the homer to Buster (Posey) was a good pitch. It was down and in and he just took a really good swing."
The victory, combined with the Dodgers' 10-4 loss at Colorado, left the Giants three games behind first-place Los Angeles with 11 to play. San Francisco snapped a three-game losing streak and remained 2 1/2 games ahead of Pittsburgh for the NL's top wild-card spot.
"Tonight was a big game," Peavy said. "We had to have it after the way we dropped the last three. I feel very blessed to feel healthy and go out there and be a contributing factor to a team that's fighting for our lives every day."
Peavy (6-4), acquired from Boston on July 26, allowed a run and five hits in 7 2-3 innings, striking out four and walking one.
In his last seven starts, he is 6-1 with a 1.13 ERA.
"You've got a good feeling each time he steps on the mound," Posey said.
Santiago Casilla pitched a perfect ninth for his 16th save in 20 opportunities.
The rest of the Giants have trouble with Collmenter's unorthodox overhand delivery. But not Posey. By going 2 for 4, including a solo homer, his career average against the Arizona right-hander is .611 (11 for 20) with three home runs.
"Who knows?" Posey said when asked to explain it. "Just one of those baseball oddities, I guess."
Collmenter doesn't understand it, either.
"I don't know, maybe the ball looks like a beach ball to him," Collmenter said. "I am not sure. Up and down, soft and hard, it doesn't matter. He seems to get the bat on it."
Posey's 21st home run of the season put the Giants up 1-0 in the fourth.
"If he hits that out I will give him credit," Collmenter said. "It was a good pitch."
The Diamondbacks tied it in the sixth when Chris Owings tripled to deep center and scored on A.J. Pollock's single.
ROOKIE ON TOP
Inciarte has made himself at home in the leadoff spot. Since June 22, he has reached base in 59 of 65 games as the leadoff hitter. At home, he's reached base in 12 straight games, hitting .354 in the process.
Crawford didn't just help the Giants at the plate. In the ninth, the shortstop ranged far to his left to field Mark Trumbo's grounder and, falling away as he threw, still got Trumbo out at first on a close play.
"What an athletic play he made there," Giants manager Bruce Bochy said. "It takes a lot of pressure off Casilla, everybody. That was one of the better plays, with what was on the line, that we've had this year."
Giants: CF Angel Pagan missed a second straight game with a sore back. Bochy said Pagan has a bulging disk and is day to day, adding that Pagan might require surgery in the offseason. ... 1B Brandon Belt, activated from the disabled list Monday (concussion), was not in the lineup Monday or Tuesday.
Diamondbacks: OF David Peralta remained sidelined with a lower back sprain. He has not played since Sept. 5.
Giants: LHP Madison Bumgarner goes for win No. 19 and the Giants try to win their seventh consecutive series at Chase Field. Bumgarner (18-9, 2.19 ERA) has won five straight, compiling a 1.80 ERA in that span with 41 strikeouts and four walks.
Diamondbacks: Manager Kirk Gibson made a late decision to start LHP Andrew Chafin instead of RHP Randall Delgado in Wednesday's series finale. Chafin will make his second big league start. He pitched five scoreless innings in the second game of a doubleheader in Cleveland on Aug. 13. Delgado was sent back to the bullpen.