Horford's surge down the stretch helped Atlanta turn back a second-half Indiana rally, which the Pacers mounted as the 6-foot-10 center was sitting out most of the third quarter with foul trouble.
Josh Smith, meanwhile, made big contributions at both ends of the court with 29 points and 11 rebounds as the Hawks won a second straight at home after dropping the first two games of the Eastern Conference quarterfinal series.
Kyle Korver contributed 19 points off the bench in the victory.
The Pacers trailed by 17 points at halftime, then cut the deficit to seven, but could get no closer and ended up falling for the 13th straight time at Phillips Arena.
Paul George led Indiana with 21 points, 12 boards and four steals.
The series now shifts back to Indianapolis for Wednesday's Game 5.