Giants 9, Diamondbacks 8: Buster Posey snapped a tie with a two-run homer in the top of the ninth inning and visiting San Francisco held on to win its season opener against Arizona.

Brandon Belt collected three hits - including a solo shot that was part of the Giants’ four-run comeback that began in the sixth inning - while Posey and Angel Pagan finished with two hits and two RBIs apiece. Madison Bumgarner was tagged for four unearned runs in four innings, Jean Machi (1-0) worked through the heart of the Arizona order in the eighth to earn the win and Sergio Romo pitched around a leadoff homer by Miguel Montero in the ninth to notch the save.

Mark Trumbo had three hits and two RBIs, Gerardo Parra drove in three runs and Montero and Chris Owings added three hits apiece for the Diamondbacks (0-3), who dropped their season-opening two-game series against the Los Angeles Dodgers in Australia last weekend. Brandon McCarthy worked 6 2/3 innings, allowing five runs on six hits.

Belt greeted Arizona reliever Addison Reed (0-1) with a one-out single to center. Reed got Pablo Sandoval to strike out swinging but left the ball over the plate to Posey, who clubbed it over the left-field fence.

The Diamondbacks built leads of 4-1, 6-2 and 7-3 in the middle innings, but their bullpen couldn’t get the final out of the seventh before the Giants tied the contest. Oliver Perez relieved McCarthy after pinch-hitter Ehire Adrianza’s two-out RBI double cut the deficit to 7-4 and allowed three straight hits before Brad Ziegler came on to yield a soft liner by Sandoval that went off the glove of Owings at shortstop to drive in another run.

GAME NOTEBOOK: Giants RHP Tim Lincecum, who was hit in the knee by a comebacker Friday night against Oakland, told reporters before the game that he expects to make his scheduled start Thursday against the Diamondbacks. … Arizona 1B Paul Goldschmidt went 2-for-5 and has hit safely in 22 straight games dating to last season. … Diamondbacks leadoff hitter A.J. Pollock went 0-for-6 with a career-high four strikeouts and stranded the tying run on second to end the game.