The Hawks have won four straight and eight of 10. Indiana, which never led, has dropped three in a row and six of seven.
Danny Granger scored 16 for the Pacers, who seemed to lose focus after coach Jim O'Brien's technical foul with 7:15 left in the third quarter.
Indiana trailed by eight when O'Brien objected to a non-shooting foul called on Tyler Hansbrough and was whistled for the technical. Johnson hit the ensuing free throw, and the Hawks ended a 17-5 run with 1:51 left in the period to take an 82-62 lead on Smith's 3-pointer.
Atlanta has won nine of 12 since Johnson returned Dec. 17 from elbow surgery.
Not long before hitting his lone 3, Smith jammed in a putback of Jamal Crawford's missed runner to make it 76-59.
Sixth man Crawford has scored at least 20 points in his last five games.
Hansbrough made his third career start and second in two nights. Coming off career highs of 23 points and 12 rebounds in Friday's three-point home loss to San Antonio, Hansbrough finished with 10 points and five boards.
The Pacers seemed flat less than 24 hours after blowing an 11-point lead in the fourth quarter against San Antonio and ending the game by missing 16 of 17 from the field. Indiana lost its seventh straight at Philips Arena and ninth consecutive in the series.
Smith and Al Horford each pulled down 10 rebounds.
Darren Collison added 13 points for the Pacers.
Notes: Mike Bibby scored 12 of his 15 in the third quarter. ... Evans was scoreless in four attempts from the field. ... Hawks G Jeff Teague, who was scoreless in 5 minutes, did not return for the second half because of a bruised hand. ... In Atlanta's 14-point home win over Indiana, Crawford scored 25 and Smith added 21.