PHOENIX -- When San Francisco right-hander Cody Gearrin jogged out to left field with one out in the 12th inning, his teammates had a simple question.

"What are you doing out here?" Gearrin was asked.

Gearrin saved the Giants' 7-6, 12-inning victory over the Arizona Diamondbacks on Friday at Chase Field by taking the mound twice in the 12th inning, once to open the inning and again after returning from left field when Javier Lopez was brought in to face one batter.

"It felt weird running out to left field from the mound and running back in, but definitely something I'll never forget," Gearrin said. "It was a first for me. It was really exciting."

Kelby Tomlinson singled in the go-ahead run in the top of the 12th inning after Brandon Belt walked and Joe Panik singled off Dominic Leone (0-1), and Gearrin entered to strike out Chris Owings leading off the last of the 12th.

Lopez entered to face Jake Lamb, who had homered off Santiago Casilla to tie the game in the 10th inning, and manager Bruce Bochy sent Gearrin to left field to replace Angel Pagan.

After Lopez walked Lamb, Gearrin went back to the mound. Lamb stole second and Paul Goldschmidt was intentionally walked before Gearrin struck out Welington Castillo and got Yasmany Tomas to ground out.

"Wow," Giants manager Bruce Bochy said.

"Cory moves around pretty good, so I was comfortable taking a little risk there. He's a gamer. He was all for it."

Joe Nathan (2-0) got the victory with a scoreless 11th inning after the Giants blew one-run leads in the seventh and 10th innings, the second time when Lamb hit his third homer of the season and fourth of his career off Casilla to tie it at 6.

"I don't know if you'll see it again," Bochy said with a smile when asked about that matchup.

Hunter Pence had four hits and scored four runs, Eduardo Nunez had two hits and two RBIs and Belt had two hits and walked three times for the Giants (75-65), who had lost 12 of 18 but still would qualify for a wild-card berth.

Brandon Drury and Kyle Jensen had two-run homers to give Arizona a 4-1 lead after three innings off Madison Bumgarner. Jensen's homer was the first hit of his career in his third at-bat.

Drury, Chris Owings, Tomas had two hits apiece for the Diamondbacks (58-82), who have lost six of eight.

Pence also made a diving catch on the warning track in right field and hit his face in the screen in front of the Giants' bullpen to take extra bases away from Jensen for the second out of the ninth inning.

The D-backs set franchise records by using 12 pitchers and 26 players in the game that lasted five hours, 23 minutes.

San Francisco took a 6-5 lead in the top of the 10th inning when Pence doubled around walks to Brandon Crawford and Belt and scored on a wild pitch by Enrique Burgos, Arizona's 10th pitcher.

Casilla could not hold that lead and has eight blown saves this season, the most in the NL.

"They are playing for their lives over there," Arizona manager Chip Hale said. "They know it. I thought our guys matched it. It just didn't come out our way."

Drury and Kyle Jensen had two-run homers to give Arizona a 4-1 lead after three innings off Madison Bumgarner. Jensen's homer was the first hit of his career in his third at-bat.

Left fielder Angel Pagan broke a 1-for-28 skid with a bases-empty homer for a 5-4 lead in the top of the seventh inning after the Giants had rallied to tie the game with two runs in the fourth and one in the sixth. Nunez had RBIs in both innings.

Arizona tied it at 5 in the seventh inning on a walk, a stolen base, and center fielder Denard Span's fielding error on Chris Owings' two-out fly ball to deep center. Owings was thrown out at the plate attempting to score.

Bumgarner gave up four runs and six hits in six innings. He struck out nine and walked one. He was in line for his 100th career victory before Span's error tied the game.

Diamondbacks starter Rubby De La Rosa was removed after 43 pitches in two innings in his first start since May 25. He was on a pitch limit after missing 14 weeks because of right elbow tendinitis.

Arizona center fielder A.J. Pollock left in the second inning after suffering a left groin injury while running out a fly ball an inning earlier.

NOTES: Giants RHP Santiago Casilla will still be used in high-leverage situations, manager Bruce Bochy said, but those could come in the eighth inning. Casilla has converted 31-of-39 save chances and has given up eight earned runs in his last nine innings, with three blown saves in 10 games. Bochy said he could use bullpen matchups when appropriate to close out games. "We're going to use everybody and put out the guy that we think is the right guy that can get us through that inning," he said. ... Arizona transferred SS Nick Ahmed (hip) to the 60-day disabled list to activate RHP Rubby De La Rosa (elbow) for his start Friday. Ahmed underwent season-ending surgery to repair a hip impingement in August. ... San Francisco has won 12 of the last 13 series at Chase Field, including a four-game sweep May 12-15. ... Giants CF Denard Span returned to the lineup after missing two games with a sore knee. ... Arizona C Welington Castillo was ejected for arguing a called third strike for the second out of the 12th inning. It was his first career ejection.