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.
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