Josh Smith added 19 points for the Hawks, who used a 16-0 run midway through the fourth to win for the 13th time in the last 15 meetings with the Raptors.
Horford reached double digits for the 31st consecutive game, the second-longest streak of his career.
He did it in 33 straight games in 2009-10.
Raptors coach Dwane Casey had suggested his team might shut down Rudy Gay after the star forward left Friday’s home loss to the Knicks with a sore back, then sat out Saturday’s loss in New York. Still sore, Gay started against the Hawks, scoring 15 points in 34 minutes and matching his season high with 12 rebounds.
Jonas Valanciunas scored 19 points, DeMar DeRozan had 14, Terrence Ross 13 and Alan Anderson 12 for the Raptors, who have lost four straight and 11 of 14.
Toronto forward Amir Johnson left with 10:28 left in the third with a left leg contusion. X-rays were negative but he did not return.
The Raptors trailed 81-80 after Anderson’s 3-pointer with 9:11 left, but Horford scored six of the next eight points, four on jump shots and two on a dunk, putting the Hawks up 89-80 with 7:26 to play.
Teague made back-to-back 3-pointers then added a driving jump shot, giving the Hawks a 97-80 lead with 4:39 left.
DeRozan snapped Toronto’s 4:48 scoreless streak with a pair of free throws, but Horford answered with a slam off an alley-oop from Teague.
Toronto shot 5 for 20 in the final quarter and was outscored 32-13.
Gay scored six in the first and DeRozan and Amir Johnson each had five as the Raptors led 25-20 after one.
Ross scored nine points in the second and DeRozan had seven, including a jump shot with less than two seconds left, giving the Raptors a 54-44 lead at the half.
Atlanta took a 71-69 lead, its first since early in the second quarter, on Smith’s 3 with 3:23 left in the third. Ross scored four of Toronto’s next six points as the Raptors reclaimed the lead, but a pair of free throws by Smith with 30 seconds left knotted the score at 75-all heading to the fourth.
Atlanta’s Kyle Korver extended his streak of game with at least one 3-pointer to 65. Korver’s streak is the fifth-longest in NBA history. Reggie Miller (68 games) had the fourth-longest, while Dana Barros tops the list with an 89-game streak.