Quentin's 12th homer of the season came in the fourth inning and padded the 4-0 lead San Diego took in the third when Chase Headley and Everth Cabrera both cracked two-run singles.
The 11-hit attack by the Padres bolstered Ross Ohlendorf (4-2), who took the victory with two runs -- one earned -- on three hits over six-plus innings.
Huston Street earned his 20th save by securing San Diego's third consecutive win.
Chicago lost its seventh in a row. Brooks Raley (0-1) took the loss in his first major league start. Raley allowed seven runs on eight hits over four innings.
Steve Clevenger and Darwin Barney had RBI for the Cubs. Josh Vitters drove in two runs with a double that was also his first career hit.