Jayson Werth added two hits including a three-run blast and posted four RBI for the Phillies, who have won eight of their last 10.
Jimmy Rollins, activated from the 15-day DL prior to the game, returned to action for the first time since April 12 and finished 2-for-4 with a double, an RBI and scored twice.
Kyle Kendrick (2-1) matched his career-best with eight innings pitched, limiting the Buccos to five hits and a pair of runs while fanning four.
Delwyn Young homered and drove in two runs for the Pirates, who have dropped five of seven.
Charlie Morton (1-7) was charged in defeat for six hits and six runs with three strikeouts over just four full frames.
The Phillies pulled in front for good with a five-run third inning.
Carlos Ruiz started with an infield single, then after Kendrick’s bunt pop to the mound, Shane Victorino was hit by a pitch. Placido Polanco singled and two batters later, Howard’s dribbler against the shift on the left side with two down put the home team ahead 3-1.
Werth followed by lining a three-run shot to right for a 6-1 game.
Ronny Cedeno began the fifth with a double, moved up on a grounder from pinch-hitter Akinori Iwamura and scored on Young’s grounder to second.
It was 7-2 for Philly in the sixth as Raul Ibanez singled, moved up on two groundouts then scored when Andrew McCutchen dropped Kendrick’s lazy fly to center.
Rollins doubled with one out in the seventh and scored on a double from Werth for a six-run edge, then Howard’s grand slam to center in the eighth made it 12-2.
Antonio Bastardo finished the rout with a scoreless ninth.
Young started the game with a blast to right, but the Phils got the run back in the home half as Victorino singled, stole second and later scored on a Rollins grounder to first.
Howard’s career high was seven RBI on June 20, 2006 against the Yankees…Philadelphia has won nine of the last 13 meetings with Pittsburgh since the start of the 2008 season…Batting in the leadoff spot, Victorino was 2-for-4 and scored three times…Kendrick had also gone eight innings in a 4-0 win at Oakland on June 25, 2008 and in a no-decision on April 20 at Atlanta…The Phils designated Wilson Valdez for assignment with the Rollins move…Phillies second baseman Chase Utley was scratched with flu-like symptoms…During the contest, the Phillies announced that reliever Brad Lidge, currently on the disabled list, received a cortisone shot on Monday and will begin throwing in the next couple of days.
05/17 22:24:07 ET