SAN FRANCISCO — Buster Posey hit a three-run homer in the first that was upheld after review and later stole a base, Ty Blach won his second consecutive start and the San Francisco Giants beat the Chicago Cubs 6-3 on Tuesday night.
Replay showed Posey’s drive to left-center had just enough to clear the wall and left fielder Jon Jay’s outstretched glove before being caught by a fan.
Blach (8-7) hit an RBI single to help his cause and the Giants snapped a four-game losing streak to the Cubs with just their third win in the last 10 against Chicago, which rallied to win Game 4 of the NL Division Series and eliminate the Giants last October on the way to a World Series title.
Blach also beat the Cubs again after a May 22 win at Wrigley Field, allowing two runs on seven hits in seven innings Tuesday with three strikeouts and a walk.
Brandon Crawford added an RBI single in the eighth after Joe Panik drove in a run on a seventh-inning groundout, then Sam Dyson closed it out for his seventh save.
Ian Happ had an RBI double and sacrifice fly as Chicago lost for only the second time in its last 14 road games dating to July 2.
Cubs starter Jose Quintana (2-2) allowed four runs — three earned — and six hits in six innings, striking out three and walking one.
He faced San Francisco only once previously, taking a loss on Aug. 13, 2014, at AT&T Park, while with the White Sox.
Joe Panik replaced injured Miguel Gomez in the top of the second.
Gomez got hurt on his first-inning groundout but there was no update on his status before the game ended.
San Francisco homered in a fourth consecutive game.
Giants manager Bruce Bochy planned to meet with struggling left-hander Matt Moore and said it was at least a possibility to skip his next turn.
“I think you have to think about it,” Bochy said.
Moore on Monday lost his fifth decision in a row and is winless in seven starts since beating the Braves on June 20.
Giants: 1B Brandon Belt (concussion) was scheduled to be evaluated Wednesday and is unlikely to go on the upcoming road trip to Washington and Miami. ... Closer Mark Melancon struck out two and allowed a hit in a scoreless inning for Class-A San Jose at Stockton as he works back from a strained forearm. ... RHP Johnny Cueto, nursing tender spots on three fingers of his pitching hand, will begin throwing this weekend.
Cubs: RHP Kyle Hendricks (4-4, 3.81 ERA) is coming off a season-high-tying seven innings last Friday against the Nationals. He also tossed seven innings in beating San Francisco on May 24 but has never won at AT&T Park.
Giants: LHP Madison Bumgarner (1-5, 2.88), who makes his sixth start since coming back from nearly three months off recovering from an April 20 dirt bike accident, is 8-2 with a 2.25 ERA in 12 career starts against the Cubs and 5-0 with a 1.74 over his last six vs. Chicago.