Giants 9, Diamondbacks 8 (10): Marco Scutaro hit a walkoff single off Bryan Shaw in the bottom of the 10th inning as host San Francisco rallied to win the opener of the three-game series.

Brandon Crawford opened the inning with an infield single, advanced to second on Brett Pill’s sacrifice bunt and moved to third on Angel Pagan’s groundout. Crawford scored easily when Scutaro singled to left field off Shaw (1-5).

Sergio Romo (4-2) earned the win with a scoreless 10th inning for the Giants, who maintained their 4 1/2-game lead over Los Angeles in the National League West.

Trailing 8-7 in the ninth, the Giants forced extra innings when Scutaro led off with a double to deep left field off Arizona closer J.J. Putz and scored on Buster Posey’s shot past third baseman Chris Johnson.

San Francisco starter Barry Zito was pulled after giving up four runs in five-plus innings and failing to protect an early lead for the second straight start. The Giants scored four runs in the first before the Diamondbacks rallied with two runs in the fifth and five in the sixth.

San Francisco jumped on Arizona starter Patrick Corbin in the first when Posey singled in a run before Hunter Pence followed with a two-run triple and scored on Hector Sanchez’s infield single.

After cruising through the first four innings, Zito gave up Johnson’s two-run homer in the fifth and started the sixth by giving up back-to-back singles to Justin Upton and Jason Kubel.

Guillermo Mota replaced Zito and promptly allowed Paul Goldschmidt’s ground rule double, which scored Upton and triggered the big inning.

Mota allowed two more run-scoring hits before being replaced by George Kontos, who immediately yielded RBI singles by Chris Young and Aaron Hill.

GAME NOTEBOOK: Giants 3B Pablo Sandoval went 3-for-5 and SS Brandon Crawford broke out of a 5-for-29 slump with three hits. … Young left the game in the eighth inning with an apparent injury after running to first base. … The Diamondbacks’ last four games have been decided by one run … Arizona RHP David Hernandez gave up two runs in the eighth, snapping a streak of 12 straight scoreless games. … Putz has worked in four of the past five games with blown saves in each of his last two appearances.