Volquez (4-5) gave up one run on four hits and struck five for his first win since May 5 and provide a welcome win for the Pads, who had lost five of their previous six games.
Rookie Jedd Gyorko had a two-run homer and veteran Mark Kotsay drove in two runs in the San Diego sixth with single to center field.
The Mariners led 1-0 after an RBI sacrifice fly by Jesus Sucre in the second inning, but San Diego scored twice in the fourth on Gyorko's homer and added a single run in the fifth.
Brandon Maurer (2-7) took the loss for the Mariners, who have lost nine of 11 games. Maurer allowed six runs – five earned – on nine hits over 5 2/3 innings.