Atlanta trailed by as many as 19 points in the second period but Horford led the comeback by making 13-of-20 shots from the field and equaling his career best with 31 points. He also grabbed 16 rebounds.
After making the dunk that gave Atlanta the lead, Horford stole the ball from Carlos Boozer and fed Joe Johnson for another slam that put the Hawks in front by three.
Both Derrick Rose and Kyle Korver missed 3-point tries for the Bulls in the final 17 seconds. Chicago had won its previous three games.
Luol Deng led Chicago with 15 points and Joakim Noah had 13 points and 12 rebounds. Rose was held to 12 points while making only 5-of-21 shots from the field.
The Bulls scored the game's first 14 points but eventually lost for the eighth time in their last nine meetings with the Hawks.