Buster Posey went 3-for-4 with two RBIs and three runs scored while Michael Morse recorded two hits and drove in two runs for the Giants, who have won 10 of 11. Jean Machi (5-0) worked two scoreless innings for the win and helped himself with a sacrifice that led to the eventual winning run, and Sergio Romo worked a scoreless 13th to remain perfect in 10 save opportunities.

Pedro Alvarez homered and drove in four runs while Andrew McCutchen collected four hits and scored twice for the Pirates, who have lost 10 games in which they have led - including three in which they were ahead entering the ninth inning. The teams combined for 36 hits, but only eight went for extra bases.

Morse doubled in a run and scored on Sanchez's single in the first to give the Giants a 2-0 advantage, but Pittsburgh put up a pair of four-run frames to take a six-run lead. Neil Walker's RBI single and Alvarez's three-run blast put the Pirates ahead in the third, and they added four more in the fifth on Alvarez's RBI single, a pair of wild pitches and Clint Barmes' sacrifice fly.

Pittsburgh starter Jeff Locke set down 13 straight batters before Angel Pagan's leadoff single in the sixth, which set off a five-run rally keyed by Brandon Hicks' two-run double. Posey singled home the tying run in the ninth and the bullpens kept it there until the 13th, when Jared Hughes (1-1) walked Pence and hit Juan Perez with a pitch before making a wild throw to first on Machi's sacrifice to allow Pence to score the go-ahead run.

GAME NOTEBOOK: Locke gave up six runs and eight hits over 5 1/3 innings in his season debut, while Giants starter Yusmeiro Petit was dinged for eight runs and nine hits in 4 1/3 frames. … The Giants were 8-for-18 with runners in scoring position, marking the first time in 20 games they have had more than three hits in those situations. … San Francisco failed to hit a home run, snapping a streak of 11 straight games with at least one.