The Phillies, who won their fifth straight and nine of 10 at home, scored five times in the first off rookie Virgil Vazquez.
Happ (6-0) welcomed the support and handcuffed the Pirates most of the afternoon. The left-hander recorded his fifth straight strong outing, compiling a 2.00 ERA during that span. Ryan Madson tossed a scoreless eighth inning and J.C. Romero worked the ninth.
Jimmy Rollins began the game with a walk, his 10th of the homestand, and Shane Victorino and Chase Utley followed with singles off Vazquez (1-3).
Ryan Howard plated the first run with a sacrifice fly to deep center. Three batters later, Feliz sent Vazquez's pitch into first few rows in left field. Philadelphia chased the right-hander, who was making his fourth major-league start, after Rollins and Victorino reached again with one out in the second.
Feliz's grand slam was the sixth of his career.
Pittsburgh's first run came in the sixth inning. Rookie-of-the-Year candidate Andrew McCutchen singled and scored on All-Star Freddy Sanchez's double.
The Pirates hit into three double plays, including the seventh, when McCutchen fell for a fake by Rollins and Utley on a fly to right, and was doubled off first base.
Left-fielder Garrett Jones led off the ninth with his fifth home run, third in three games.
Solid pitching and a resurgent offense has contributed to Philadelphia's best homestand since May 31-June 12, 2005, when they went 12-1. The Phillies (48-38) enter the All-Star break and a comfortable lead over the second-place Marlins.
At the break last year, Philadelphia was 52-44 and a half game ahead of the New York Mets.
NOTES: Pirates left-hander Zach Duke was named to the NL All-Star game. He replaces San Francisco's Matt Cain, who was hit below his right elbow with a line drive on Saturday. ... The Phillies cavalcade of All-Stars received rousing applause before Sunday's game. Philadelphia sends Howard, Utley, Jayson Werth, Shane Victorino and Raul Ibanez, plus manager Charlie Manuel and his entire coaching staff. ... The Phillies are 17-9 in day games, best in the NL.
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