In the closing seconds, without a timeout, Atlanta missed two 3-pointers but grabbed two offensive rebounds before fumbling the ball away, which led to Mitchell’s free throws.
Clark had four 3-pointers, tying the rookie-season record of 85 by Atlanta’s Rhyne Howard in 2022.
"Our chemistry has improved," Clark said of the Fever's recent play, adding that for her individually, she is "really excited because I feel like there's so many areas for me to continue to get better, and that's exciting as a player."
Atlanta (10-19), which started the day a half-game out of the final playoff spot, trailed by 18 early in the second half when Clark hit a 3-pointer before outscoring the Fever (14-16) 41-32. The Dream got within two before Indiana’s five-point possession blunted the rally.
Tina Charles scored 21 to lead Atlanta, which moved the game to the home of the Atlanta Hawks and set an attendance record of 17,608, surpassing the crowd that showed up for the previous contest against the Fever (17,575). Howard had 16 points, Allisha Gray added 12 -- none after receiving a flagrant foul from Boston midway through the third quarter -- and Jordin Canada scored 10 for the Dream.
Howard's 3 pulled Atlanta to 76-74 with 4:13 to play, but after grabbing an offensive rebound, Clark found Lexie Hull for an and-1 layup a minute later. Hull rebounded her missed free throw and fed Mitchell for an and-1 layup that she converted for an 81-74 lead.
Nia Coffey made a 3 for Atlanta with just under a minute to play to make it 82-79.
Mitchell had 15 points and Boston 12 on combined 12-of-21 shooting as the Fever took a 52-38 halftime lead.
According to ESPN Stats & Information, Mitchell has 105 points combined over Indiana’s past four games, equaling the record she set last year for most points in a four-game span in Fever history.
At halftime, the gold medal team from the 1996 Atlanta Olympics was honored.
Information from The Associated Press was used in this report.