The surprising rally boosted the Cavaliers to just their second road win in 11 tries this season and ended a four-game losing streak. Atlanta had won six games in a row before faltering down the stretch.
Atlanta's lead stood at nine points entering the fourth quarter, but Cleveland moved in front by three with 16 seconds to play on Anderson Varejao's two free throws. Lou Williams then tied it by hitting a 3-pointer with 14 seconds left.
Cleveland worked the ball to Dion Waiters for a 3-point attempt that bounced off the rim with 3 seconds remaining, but Gee was there to grab the offensive rebound and produce the winning points.
Jeremy Pargo scored 22 points for the Cavaliers, who outrebounded the Hawks by 21. Waiters added 21 points and Varejao had 20.
Josh Smith paced the Hawks with 25 points and eight rebounds.
Swim Week Miami Beach 2014 [PHOTOS]