SAN FRANCISCO — Brandon Belt's RBI single with one out in the bottom of the 10th inning gave the San Francisco Giants a 3-2 victory over the Colorado Rockies on Monday night, their second straight walkoff win.

The defending World Series champions, however, were eliminated from contention in the NL West on Monday when the Los Angeles Dodgers beat the Arizona Diamondbacks.

Angel Pagan hit a one-out single off reliever Adam Ottavino (1-3) and took third on Marco Scutaro's single. Belt, who doubled in the tying run in the eighth, hit a 1-2 pitch over the head of left fielder Charlie Culberson for his second game-ending hit this season.D.J. LeMahieu singled and doubled to extend his career-high hitting streak to 11 games, and Nolan Arenado scored from second base on an infield groundout for the Rockies.

Buster Posey hit his 15th home run of the season for San Francisco, which was kept in check offensively most of the game by Colorado starter Jhoulys Chacin.

Chacin struck out five and walked one over seven innings, lowering his ERA in 12 starts on the road to 2.10. The right-hander retired 16 of the final 18 he faced and left with a 2-1 lead. Colorado's bullpen couldn't make it hold up.

Pagan reached on a one-out infield single off Matt Belisle and took second when Arenado's throw from third sailed past first base for an error.

After Scutaro's groundout moved Pagan to third, Belt doubled to right to drive in Pagan with the tying run.

Tim Lincecum allowed two runs over eight innings. The right-hander struck out three and walked one.

The Rockies scored their first run after a defensive breakdown by the Giants.

Arenado doubled in the second and was headed for third on Yorvit Torrealba's slow roller between the mound and first base when he noticed no one covering home. Arenado quickly scampered home, and with no one covering, San Francisco first baseman Belt's throw sailed to the backstop.

After Posey's homer tied it, the Rockies made their own defensive gaffe.

As fog drifted over the waterfront ballpark, Pablo Sandoval lofted a high fly ball to left center. Colorado's Corey Dickerson ran toward the warning track but inexplicably stopped and let the ball drop in as Sandoval raced to second with a double.

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PETIT EYES AN ENCORE

San Francisco's 28-year-old right-hander Yusmeiro Petit will make his first start since coming within one out of tossing a perfect game on Friday when he takes on the Rockies on Wednesday afternoon.

Petit is 3-0 with a 2.05 ERA for the Giants.He has 30 strikeouts and just four walks in 26 innings pitched this season as he tries to make a run at earning a spot in the 2014 starting rotation.

Petit is 13-20 with three big league teams. He has pitched in 76 games and 260? innings. His 5.16 ERA goes with a career WHIPof 1.39. He has an 0.91 WHIPthis season with San Francisco.Juan Nicasio (8-7, 4.68) will face Petit for Colorado.

The Giants' Ryan Vogelsong (3-5, 5.62) will take on the Rockies' Jorge De La Rosa (16-6, 3.31) today at

7:15 p.m.