Buster Posey followed Brandon Belt's leadoff triple in the sixth with a go-ahead double, Jake Peavy won for the second time in six starts, and the San Francisco Giants beat the Cubs 4-2 on Wednesday night to stop Chicago's six-game winning streak. Kelby Tomlinson added an RBI double of his own in the sixth against Kyle Hendricks as the Giants ended a three-game slide with their second victory in seven games. Nori Aoki homered for San Francisco.