Vandersloot also had seven rebounds and six assists, and Stewart added four steals and three blocks. Sabrina Ionescu scored 11 points on three-for-12 shooting and Jonquel Jones had nine points and eight rebounds for New York (20-6).
New York trailed 54-50 entering the fourth quarter before holding the Sparks to 15 points in the final 10 minutes.
Nneka Ogwumike scored with 14.1 seconds left for Los Angeles’ only field goal in the final three minutes. But Vandersloot made one of two free throws for a 74-69 advantage.
Ogwumike had 20 points and eight rebounds for Los Angeles (9-17) and moved past Candace Parker (5,684) for the second-most points in franchise history, trailing Lisa Leslie (6,263).
Jordin Canada added 13 points and six assists, and Layshia Clarendon scored 11 points for Los Angeles.
Canada had a game-high nine points in the first half as Los Angeles led 34-32. Both teams shot less than 39% from the field in the opening 20 minutes.