All that talk about Buster Posey's second-half power drought was answered with one mighty swing in a September game that mattered, and his two-run homer helped the San Francisco Giants beat the St. Louis Cardinals 8-2 Friday night in a matchup of playoff contenders. Posey drove in four runs and the Giants stayed four games back of the NL West-leading Los Angeles Dodgers, who won at Arizona. San Francisco maintained its one-game lead over the New York Mets for the league's top wild card, moving three games up on the Cardinals in the wild-card standings.