The win was San Diego's second in a row and dealt a blow to the NL West rival Dodgers, who trail St. Louis by 4 1/2 games in the race for the second wild card berth.
Volquez (11-11) held Los Angeles to six hits and struck out four. Houston Street allowed a run in the ninth but stranded two runners for his 23rd save.
Yasmani Grandal drove in a run for San Diego and Chase Headley collected two hits.
A.J. Cruz drove in the lone Dodgers run with a double in the ninth. The Dodgers outhit the Padres 10-5.
Josh Beckett (1-3) allowed two runs -- one earned -- on five hits and struck out seven in 5 2/3 innings.