Doumit's first-inning sacrifice fly gave the Pirates a 1-0 lead and his two-run homer in the third put Pittsburgh up 3-0. After McCutchen socked a solo shot in the fourth, Doumit struck again, driving in a run on a ground-rule double to put the Pirates in control 6-0.
McCutchen also doubled and hit two singles while Neil Walker went 2-for-3 with a triple, an RBI and two runs scored to help the Pirates win for the third time in four games.
Paul Maholm (4-4) surrendered two runs on six hits over 6 1/2 innings to notch the victory.
Todd Wellemeyer (3-5) didn't make it past the third inning for the Giants, getting tagged for six runs on nine hits.