Chase Headley drew a one-out walk from Brandon Lyon (0-2), stole second, and then came home when Quentin sliced a pitch that bounced off the right field wall.
The blow handed the victory to Dale Thayer (1-2), who had tossed a scoreless top of the 10th. Huston Street picked up his 11th save as the Padres took the opener of a four-game series.
Jesus Guzman socked a two-run homer in the eighth to give the Padres a 7-6 lead before Luke Gregerson blew a save opportunity by surrendering a game-tying homer to Jason Castro in the bottom of the frame.
Brian Bixler and Carlos Lee also went deep for the Astros.