SAN FRANCISCO (AP) — Buster Posey hit a go-ahead RBI single in the eighth inning, and the San Francisco Giants beat the Colorado Rockies 3-1 on Monday night to match their best winning streak of the season at three games.

Gregor Blanco hit a tying home run leading off the sixth for San Francisco and also added a pair of singles, including one to start the rally in the eighth against loser Rex Brothers (1-2). Joaquin Arias then beat out an infield single when Rockies catcher Wilin Rosario tried to let the bunt up the first base line roll foul and it stayed fair. He rushed his throw to first and the ball got past Todd Helton for an error that moved Blanco to third.

Sergio Romo (2-0) struck out Michael Cuddyer with runners on second and third to end the eighth for the win. Santiago Casilla finished for his eighth save in nine chances despite allowing an unearned run in the ninth.

Casilla retired Chris Nelson on a groundout to end it with the bases loaded.

The Rockies got a scare in the eighth when Troy Tulowitzki took a foul ball hit by teammate Dexter Fowler off the left leg.

After being examined by athletic trainer Keith Dugger, Tulowitzki stayed in the game and took his at-bat. The star shortstop reached on an infield single against Javier Lopez but hobbled to the base, clearly in pain. Manager Jim Tracy and Dugger hustled out to first and Tulowitzki was lifted for pinch-runner Nelson.

Brett Pill singled in an insurance run in the eighth for the Giants after he couldn’t come through earlier.

In the sixth, Posey hit a two-out single and Angel Pagan doubled to bring up Pill with runners on second and third, but he struck out. Posey snapped an 0-for-10 funk with just his fourth hit in 28 at-bats.

Rosario hit a towering home run deep into the left-field bleachers to start the fourth for Colorado, which missed several other scoring opportunities in losing its fourth in a row and ninth in 10. The Rockies are wrapping up a rough eight-game road trip with this short two-game series.

Christian Friedrich delivered the kind of outing Colorado desperately needed in just his second career start. The left-hander struck out 10 and walked one, allowing six hits and one run in seven innings. He won in his major league debut last Wednesday, allowing two runs — one earned — on five hits with seven strikeouts and one walk in six innings at San Diego.

His consistency came at a good time for Colorado. A day earlier, the Rockies walked 10 batters, all during a span of five innings, and six of them scored in Sunday’s 11-5 road loss to the Los Angeles Dodgers that led to a sweep.

Friedrich got a nice over-the-shoulder catch from second baseman Marco Scutaro on which he hustled back into shallow left to snag Melky Cabrera’s flyball.

Giants starter Ryan Vogelsong walked a season-high five batters and allowed three hits in seven innings. He still hasn’t lost to the Rockies for his career, going 4-0 with a 1.07 ERA in five starts, including 3-0 with a 0.64 ERA in four at home.

The right-hander walked three in the first and two more with two outs in the third to load the bases. Vogelsong received a mound visit from pitching coach Dave Righetti before facing Michael Cuddyer

The Giants ended a stretch in which they had lost the first game of a series in the previous six openers. San Francisco is just 4-8 in those games this year — with this win marking the club’s first victory in a series opener since beating the Mets on April 20 in New York.

Cabrera had his 11-game hitting streak snapped with an 0-for-4 night for the Giants.

NOTES: Giants slugger Pablo Sandoval had five stitches removed from his surgically repaired left hand. He had surgery May 4 for a broken hamate bone. ... San Francisco 2B Freddy Sanchez was scheduled for an MRI on his lower back after injuring it in his rehab games. ... Fowler didn’t start as a precaution a day after he left the game following the fourth inning because of blurred vision, the result of a throw to second by catcher A.J. Ellis that struck him as he advanced. He was checked for a concussion. ... The Giants sold out their waterfront ballpark for the 100th straight game dating to the final series of the 2010 season against San Diego. ... San Francisco’s Aubrey Huff, activated last Monday from a 15-day DL stint for anxiety disorder, could get a start soon. “He’s close,” manager Bruce Bochy said. “He told me he’s a lot better.”