Brandon Crawford opened the bottom of the 10th with an infield chopper for a single, advanced to second on a sacrifice bunt from Brett Pill and moved to third on a groundout from Angel Pagan. Scutaro drilled a 3-1 cutter from Arizona reliever Bryan Shaw down the left-field line to drive in Crawford for the game-winning run.
"It's always exciting to get a walk-off, but the important thing was that it was a great team effort," Scutaro said. "We never gave up and we just kept fighting. We didn't put our heads down and we just kept fighting and played hard until the very end."
The back-and-forth affair began with the Giants posting a four-run first inning, only to watch as the D-backs scored five runs in the sixth and another in the eighth to claim an 8-5 lead. The Giants trimmed the lead to one run in the bottom of the eighth with two-out doubles from Hector Sanchez and Crawford and a pinch-hit RBI single from Brandon Belt.
Scutaro had earlier sparked the Giants' game-tying rally in the ninth with a leadoff double to left off Arizona closer J.J Putz, later coming around to score on Posey's line-drive double to left to send the game into extra innings.
"I just go up there with a plan and look for a good pitch to hit, and sometimes it works, and sometimes it doesn't," Scutaro said, shrugging off observations of his propensity for clutch hits.
The walk-off win comes after the Giants took five of six in their recent road trip, and the resilience shown by the team wasn't lost on anyone in the clubhouse as the Giants gear up for the final stretch of the season that will solely feature National League West opponents.
"There's a lot more attention on these games now, and every game is intense," Bochy said. "Both teams fought hard, and it's a little bit different in September, there's no getting around it."
"They're playing well right now, they've got all the momentum going and we're not," Putz said.
The Giants picked up their sixth straight win in a Barry Zito start for the first time since he signed with the team before the 2007 season.
"We're just showing a lot of fire right now," Zito said. "We're showing a lot of character. We just keep playing; we're relentless."
Zito was solid for five innings and took a 4-2 lead to the hill in the sixth, but the lefty was lifted with two runners on and no outs and the bullpen couldn't stop the bleeding.
The D-backs opened the sixth with back-to-back singles from Justin Upton and Jason Kubel, prompting Bochy to replace Zito with Guillermo Mota. Paul Goldschmidt's ground-rule double to left-center knocked in Upton, and Kubel tied the score when he came home on Chris Johnson's sacrifice fly to center before Arizona went ahead on Willie Bloomquist's RBI single to left. Mota was pulled for George Kontos, who allowed RBI singles to Chris Young and Aaron Hill.
Zito had held the D-backs to just two baserunners through the first three innings, but gave up a two-run home run to Johnson in the fourth and was charged with two more runs after allowing back-to-back singles before exiting with no outs in the sixth.
"He was throwing great and he was hitting his spots," Bochy said. "He started leaving some pitches up and they started getting some two-strike hits off him."
The Giants are now winners of 13 of their last 17 games, and their season-high 19 games above .500 is the most since they were 23 games above .500 at the end of the World Series championship season in 2010. And though they blew a four-run lead for just the third time this season, the Giants picked up their fourth win in which they trailed heading into the ninth inning.
"Every game is huge, as we know, but you're going to lose a few," Zito said. "When there are some games that seems like you're going to lose, but when you come back and win, that's just in the bonus column. Those are the ones that will make the big difference when the year is over, the ones that we kind of scrapped and ended up taking it."