Matt Duffy hit a three-run double in San Francisco's decisive six-run third inning, Jake Peavy worked into the sixth to end a three-start winless stretch, and the Giants beat the Nationals for the third straight game with a 12-6 win Saturday night. Ian Desmond cleared the left field bleachers with a second-inning leadoff home run that hit the walkway for one of the longest in the ballpark's 16-year history. It was estimated at 470 feet, the Giants said.