89-81 on Saturday night.
Paul Pierce scored 17 of his 26 points in the third quarter as the Celtics erased a 19-point deficit and went on to consecutive wins for the first time since late November against Oklahoma City and Orlando.
Boston, which beat Indiana 94-75 on Friday night, had lost four straight road games.
Lou Williams scored 21 of his 28 points in the first half for Atlanta, which has lost two straight. Jeff Teague added 17 points, and Josh Smith, who was 2-for-12 in the second half, finished with 12 points and 10 rebounds.
The Hawks got off to a fast start, then fell apart in the third quarter as Boston began doubling ballhandlers on the perimeter and clamping down on Atlanta inside.
The Celtics trailed by 19 with 6:20 left in the second, but went up 61-60 on Jared Sullinger’s alley-oop layup with 3:47 left in the third. It was their first lead since the game’s first minute.
Boston opened the third with a 14-1 run to pull within one. Hawks coach Larry Drew, whose team missed its first five shots from the field to begin the second half, called timeout at the 7:29 mark, but Teague lost the ball out of the bounds on the ensuing possession.
Atlanta was just 2-for-14 from the field in the third and trailed 71-62 heading to the final period.
Kevin Garnett’s fast-break layup with 8:53 remaining gave the Celtics their first double-digit lead at 79-68. Garnett finished with 14 points.
Williams outscored the Celtics 13-10 by the 5:47 mark of the first and hit his first seven shots from the field. His 16th point came on a layup for Atlanta’s first double-digit lead at 23-12 late in the first.
But the Hawks could not overcome the absence of injured shooting guards Devin Harris and Anthony Morrow, and it hardly helped that Kyle Korver fouled out with 6:37 remaining and DeShawn Stevenson played only 13 minutes because of sore knees.
NOTES: Korver fouled out for the first time in 27 games this season and finished with nine points. ... Atlanta scored 31 points in the first quarter, tying for the highest by a Boston opponent and the most since the Celtics opened the season Oct. 30 at Miami. ... The Hawks’ nine points in the third were a season low by a Boston opponent. ... Harris missed his ninth straight game with a sore left foot. ... Morrow was sidelined for the fifth straight game because of a strained right hip.