Burriss began the inning with a single off Chris Resop (0-1) and went to third on Ryan Theriot's pinch-hit single. The Pirates then intentionally walked Angel Pagan to load the bases and set up a force-out at the plate.
Melky Cabrera seemed to comply by smacking a grounder to shortstop Clint Barmes, but his throw home was low, allowing Burriss to score the game-winner.
Burriss and Nate Schierholtz each went 2-for-4 with an RBI for the Giants, who received word before the game that closer Brian Wilson may be lost for the season with elbow problems.
Neil Walker had two hits, including a two-run single, for the Bucs.