Pence's bases-loaded shot came in the fifth inning and handed the Giants a 12-1 lead. He hit a two-run single to ignite a four-run second.
Belt finished 5-for-6 with four runs scored while Gregor Blanco went 3-for-4 with three runs scored and an RBI for San Francisco, which rapped out 22 hits in taking a second straight from the Dodgers.
Tim Lincecum (10-13) went six innings, allowing three runs on five hits. He walked two and struck out six.
LA starter Ricky Nolasco (13-10) was pounded for seven runs (five earned) on seven hits in just 1 1/3 innings.
Alex Castellanos hit his first major-league homer for the National League West-leading Dodgers.