The Phillies had a chance to send the game to the 12th inning, but shortstop Freddy Galvis made a throwing error on what would have been the third out of the inning. The error put runners on second and third and brought Harrison to the plate.
Harrison hit the first pitch he saw from Jonathan Papelbon right back up the middle for a walk-off single.
It was Pittsburgh's fourth straight win and its second walk-off victory of the three-game series against the Phillies. Philadelphia has lost six in a row and nine of its last 10.
After his game-winning hit, Harrison got a pie in the face from teammate A.J. Burnett.
- Dan Gartland