Joaquin Arias drove in five runs with two doubles and a homer Wednesday, leading San Francisco to an 8-4 win and a three-game sweep of the Los Angeles Dodgers. The Giants began the crucial series a half game behind the Dodgers and emerged with a 2 1/2-game advantage nearing the final month of the regular season. Arias came into the game with two home runs and 21 RBI in 246 at-bats this season, but erupted with a big night that included three of the Giants\' eight hits. Angel Pagan opened the San Francisco first with a double off Chris Capuano (11-9) and moved to third on a single by Marco Scutaro. Pablo Sandoval\'s sacrifice fly delivered Pagan with the first run of the game and Arias then hit a two-out homer to right to make it 3-0. Arias doubled home another score during a three-run sixth and he added a two-run double in the seventh. Matt Cain (13-5) allowed a run on seven hits with five strikeouts over seven innings to get the win. It was Cain\'s third win in as many starts after he had failed to pick up a victory in six straight appearances. The Dodgers scored three runs in the eighth on an RBI double by Matt Kemp and a two-run single by Luis Cruz.