Riquna Williams added 13 points for the Sparks (3-2).
Kelsey Mitchell led Indiana (2-3) with 24 points, Candice Dupree scored 16 and Teaira McCowan 13.
Gray converted a three-point play to give Los Angeles the lead for good at 10-7. The Sparks used a 10-0 run to take an 18-point lead midway through the third quarter and led by as many as 21.
L.A.'s Nneka Ogwumike left the game with a minor hamstring injury. She had four points and two rebounds in 13 minutes.