It was Atlanta's first victory without star Angel McCoughtry, who the team announced just before the game that she would miss the remainder of the season due to torn ligaments in her left knee. She was averaging 16.5 points, including a career-high 39 points at New York earlier this year.
Bentley finished with 13 points and Elizabeth Williams had 10 points and seven rebounds for Atlanta.
Atlanta (20-10) is 2 1/2 games behind first-place Seattle (23-8) and a game ahead of third-place Washington (19-11). The Storm have clinched a top-two seed and will receive a double-bye to the semifinals.
Bentley made a 3-pointer to give Atlanta a 71-68 lead and she came off a high screen to drain a long jumper to make it 75-70. Riquna Williams answered with a 3-pointer to pull Los Angeles closer but Tiffany Hayes secured it at the free-throw line with 4.4. seconds left.
Candace Parker had 20 points and 12 rebounds for her 11th double-double of the season for Los Angeles (18-12). Williams added 18 points off the bench and Chelsea Gray had 13 for the Sparks, who were playing the second-half of a back-to-back after winning in New York on Wednesday night.