Jeff Teague scored 25 points for the Hawks, while Horford finished with 17 points and 12 rebounds.
The Mavericks were up 70-55 when point guard Jose Calderon went out late in the third quarter with an injured right ankle. X-rays were negative but he did not return.
Without Calderon running the offense, Dallas totally bogged down. Rookie guard Shane Larkin had a miserable night, going 0-for-4 from the field and turning it over four times. The Mavericks hit just 38 percent, with Vince Carter missing badly on the final shot of the game.
Atlanta snapped a three-game losing streak and climbed back above .500 at 9-8.
The Mavericks was just 3-of-19 in the final quarter, their last field goal coming on Shawn Marion’s jumper with 5:05 remaining for an 85-77 lead. Dallas managed only two more points the rest of the way, a pair of free throws by DeJuan Blair with 3:27 left.
Atlanta scored the final seven points, capped by Horford’s 20-foot jumper after the defense sagged off him near the top of the key.
Calderon and Dirk Nowitzki led the Mavericks with 16 points apiece, while Marion chipped in with 15.
Lou Williams made his first start for the Hawks since coming back from knee surgery that kept him out much of last season and the first few weeks of this season. He scored a season-high 12 points.
But Teague carried much of the load, bouncing back from a four-point effort in a loss to Houston. He kept getting to the foul line, doled out six assists and didn’t turn it over until he lost the ball out of bounds with about 2½ minutes remaining.
The Hawks jumped out to a 23-18 lead in the first quarter, but the Mavericks scored the final 10 points of the period to lead at the break. Dallas got much of its production beyond the arc, going 6-of-7 from 3-point range. Calderon went 3-for-3, Marion hit a pair of long-range jumpers and Carter chipped in with one.
Nowitzki missed all three of his shots and was held scoreless in the opening quarter. But he warmed up in the second, knocking down Dallas’ first six points for a 16-0 run that extended the lead to 34-23.
The Mavericks maintained a double-digit lead through most of the second and third quarters, going to the final period up 75-64. Their biggest lead was 66-49 midway through the third.
NOTES: Kyle Korver skipped his second straight game with bruised ribs, again delaying his quest to set an NBA record for consecutive games with a 3-point basket. He remains at 88 in a row, one shy of the mark set by Dana Barrow from Dec. 23, 1994-Jan. 10, 1996, with Philadelphia and Boston. Korver was receiving treatment during the game, but the Hawks weren’t sure if he’d be on a road trip to Washington and San Antonio. ... Dallas C-F Brandan Wright (fractured left shoulder) is getting closer to practicing. “Hopefully it doesn’t flare up,” Wright said before the game. “We’ll keep pushing it each and every day.” ... Former Hawks G Devin Harris is recovering from left foot surgery and didn’t get a chance to play against his old team.