The Mavericks did not make a field goal during the final 5:05 while Atlanta was closing the game on a 21-7 run.
After trailing by 17 points in the second half, the Hawks ended a three-game losing streak and climbed back to the .500 mark.
Horford's game-winning shot gave Atlanta its first lead since the opening quarter. Vince Carter then missed an attempt for Dallas, leaving the Mavericks with just 12 points in the final period.
Notable deaths of 2014 [PHOTOS]
Arizona Cardinals player formally charged