SAN FRANCISCO -- Buster Posey drove in a pair of runs, Jake Peavy pitched five scoreless innings and the San Francisco Giants beat the Oakland Athletics 3-0 on Friday night.Gregor Blanco also drove in a run for the Giants. Chris Heston,George Kontos, Hunter Strickland and Santiago Casilla each followed with a scoreless inning. Samardzija Tosses Five Scoreless as Giants Best A's at AT&T A's starter Kendall Graveman gave up two runs on four hits in his five innings. Mark Canha's double was the hardest hit ball of the night for Oakland.Peavy allowed two hits, walked one and struck out three. SF Ordinance Bans Chewing Tobacco at AT&T Park Denard Span led off the first with a single and Joe Panik walked ahead of Posey's double.Photo Credit: AP