Five Houston runners reached base -- three on walks and one on an error. The only hit off Volquez came when Matt Downs beat out an infield single in the fourth inning.
Volquez (6-7) is in his eighth major league season, his first with the Padres. The one-hitter came in his 110th career start.
The Padres won the final three games of the four-game series.
Alexi Amarista opened the San Diego first inning with a double off Lucas Harrell (7-7) and scored the game's only run on Logan Forsythe's single.
Harrell allowed only three other hits and struck out six over seven innings.
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