Candace Parker added season highs of 18 points and 13 rebounds for the Sparks (7-11), and Lisa Leslie finished with 15 points.
Lauren Jackson scored 21 points before fouling out for the Storm (12-9), which has lost three of four. Swin Cash, Camille Little and Tanisha Wright each had 14 points. Cash also had eight rebounds, and Wright had six assists.
The Storm led 72-66 with 3:18 left in overtime, but the Sparks used a 12-0 spree to move ahead 78-72 with 14.2 seconds to play. Quinn scored eight points during the run, including a 3-pointer that gave Los Angeles a 74-72 lead with 1:01 left.