"I think it showed growth from our team being in a position where they made a run at us and we needed to score," Horford said. "Guys scored some key points. We got stops when we needed to. That was a game where we got better."
Lou Williams had 21 points and a career-high 12 assists, Horford added 20 points and Atlanta won its fourth straight.
David West scored a game-high 29 points for the Pacers, who had won four in a row and seven of eight.
Smith, Atlanta's leading scorer this season, watched the game from the bench as Zaza Pachulia made his seventh start of the season and responded with 17 points and a game-high 14 rebounds.
Williams, who signed in the offseason to be the Hawks' sixth man, had his first career double-double. Rookie John Jenkins scored a career-high 10 points, and Ivan Johnson shook off flu-like symptoms to add six points and six rebounds.
Injuries to reserve guards Devin Harris and Anthony Morrow left Atlanta coach Larry Drew with just nine players in his rotation, but Indiana never got closer than three in the fourth quarter after Paul George's three-point play made it 91-88 at the 5:18 mark.
Jeff Teague's floating runner made it 101-90 less than 3 minutes later. Teague scored 10 of his 15 points in the final period.
"From a production standpoint, everybody gave a little something," Drew said. "We did what we had to do, particularly on the defensive end. We had to make a lot of adjustments as the game went on to try to keep them off-balance a little bit."
Pachulia and Horford combined to hold Pacers center Roy Hibbert to no points, one rebound and one blocked shot in 20-plus minutes. Hibbert was such a non-factor that Indiana coach Frank Vogel kept him on the bench in the fourth quarter.
"I love the kid," Vogel said. "He has great heart, gave great effort. He didn't have it tonight."
West gave Atlanta fits for much of the game, twice hitting 3-pointers at the shot-clock buzzer, but his offensive movement away from the ball opened up chances for teammates and helped him find good looks to score 11 points in the fourth.
"We knew David West had it going," Teague said, "so we just had to try to do our best to let him see a double-team and a wall, and we got some big stops."
George finished with 18 points and George Hill added 15 for Indiana. Hill started and played 33 minutes despite a sore right groin.
West liked the Pacers' chances before the game with Smith, Harris and Morrow unable to play. It just didn't work out the way he had hoped.
"Even though we had it close, they controlled the game from start to finish," West said. "They were locked in offensively. We just couldn't put up a big enough fight to slow them down."
Kyle Korver scored five points in a single possession late in the third to push the lead to 12 points.
After officials watched a video replay, the call was upheld that Lance Stephenson committed a flagrant foul on Korver, pushing him to the floor on a play away from the ball. Korver hit both free throws and then a 3-pointer at the 4:10 mark to make it 77-65.
"He purposely ran at me," Korver said. "I saw him coming. I knew he was going to hit me like that. I just took it, you know? But he put a shoulder into my chest."
The Hawks' lead swelled to 18 with 2:12 remaining in the third on Johnson's putback.
Horford, who played 37 minutes despite a right hip contusion, hit a 17-footer to make it 93-88 with 5:02 remaining.
Indiana never led after Korver's 3-pointer made it 18-16 at the 4:13 mark of the first.
Smith was injured in Friday's win at Cleveland. Drew listed his status as day to day. ... Stephenson was helped off the floor with 5:44 remaining after getting hit on the left side of the face. ... Atlanta has won 11 straight at home over Indiana and four straight overall. ... Harris missed his six straight games with a sore left foot. ... Morrow is recovering from a strained right hip after getting hurt at Cleveland. ... Pacers reserve G Sam Young did not travel with the team because of the flu. ... Atlanta is 4-0 with Williams in the starting lineup.