SAN FRANCISCO (AP) -- Hunter Pence came through in a big way, erasing a slow start with his new team with one swing of the bat.

Pence hit a three-run homer during a five-run rally in the eighth inning that lifted the San Francisco Giants over the Colorado Rockies 9-6 on Sunday.

''He hit the ball hard the one time that was turned into a double play,'' Giants manager Bruce Bochy said. ''That three-run homer makes up for a few mistakes we made.''

Buster Posey's sacrifice fly in the eighth tied it. Melky Cabrera, who had an RBI single in the comeback, drove in three runs.

Brandon Belt doubled twice and went 4 for 4 for the Giants.

''A lot of stuff was going wrong for us but it didn't matter,'' Belt said. ''That home run came at a great time.''

Matt Belisle (3-4) took the loss after allowing the first three hitters he faced to reach base. Rafael Betancourt gave up Posey's deep fly to left and Pence's drive into the left-field bleachers.

Clay Hensley (4-3) pitched the eighth for the win.

Eric Young had three hits and drove in a run for the Rockies, who have lost three of four. Starting pitcher Alex White and reliever Carlos Torres also drove in runs.

''We did everything we could to try and win that game,'' Rockies' manager Jim Tracy said. ''We played with heart and we played with energy. The key to the whole eighth inning is when the leadoff pop up fell. I really believe that if we record that out, that inning was going to go cleanly. I believe that. We opened the door for them.''

Giants starter Barry Zito lasted 5 1-3 innings, giving up four runs and seven hits. White allowed three runs and seven hits in four innings.

''We just made a mistake in the first inning,'' White said. ''I just wanted to keep us in the game.''

The Giants trailed 6-4 when Brandon Crawford singled, pinch-hitter Hector Sanchez doubled and Angel Pagan walked to open the eighth. After Belisle got Marco Scutaro on a short fly to left, Cabrera delivered an infield single to score a run.

Betancourt came in to face Posey, who fouled off five consecutive pitches before the sacrifice fly. Pence, hitting .137 as a Giant, then hit his 18th home run.

''That was big,'' Posey said. ''He's been working hard and it was nice to see him come through.''

Torres delivered a two-out single, his first career hit, to highlight a two-run rally in the sixth that put the Rockies ahead 5-4. D.J. LeMahieu doubled home run a batter earlier.

Cabrera's two-run single in the first gave the Giants the early lead. Belt also singled home a run in the inning.

Young and Josh Rutledge each doubled home a run in the third and White's sacrifice fly in the fourth tied it at 3.

Ryan Theriot's double put the Giants back on top in the fifth, setting up Torres' hit in the sixth.

NOTES: White recorded his first career RBI. ... The Giants expect INF Pablo Sandoval to be available Monday night against the Washington Nationals after playing in his third rehab game at Class-A San Jose. ... RHP Ryan Vogelsong (10-5, 2.27) goes for the Giants against the Nationals. He leads the NL in ERA. ... LHP Jeff Francis (3-4, 6.06) pitches for the Rockies against the Milwaukee Brewers.