Al Horford finished with 22 points and 15 rebounds as the Hawks earned home-court advantage in the first round of the playoffs. Atlanta needed either a win or a loss by Miami, which fell by seven in Boston, to wrap up the No. 4 spot.
"Words cannot describe how I feel," said Smith, the only holdover from a team that managed just 13 wins in 2004-05. "Even last year, making the playoffs, people were counting us out, saying we weren't even going to even make the playoffs this year, but we proved them wrong."
Indiana, which had won two straight and four of five, was eliminated from playoff contention.
The Hawks won their third straight, all against sub-.500 teams, and are assured of home-court advantage in the first round of the playoffs for the first time since winning a best-of-five series against Detroit in 1999.
Danny Granger had 35 points to lead the Pacers in scoring for the eighth straight game. Jarrett Jack, who finished with 17, matched Indiana's biggest lead at seven midway through the third, but the Hawks never trailed after Johnson hit two free throws to make it 76-74 with 4:04 left in the quarter.
"Hopefully we'll be able to come back next year and get our franchise back on top," reserve center Jeff Foster said. "Our intentions were to win this game, although our playoff chances were very slim. These last four games, we've been trying just to see what happens, but unfortunately we're not in the same position the Hawks are in."
Mike Bibby hit a 3 with 4:24 left to give the Hawks a 12-point lead, the game's biggest, at 113-101. Jack's 3-pointer with 21 seconds remaining cut it to 121-118, but Horford hit one of two free throws to end the scoring.
Atlanta coach Mike Woodson, in his fifth season, has increased his victory totals from 13 to 26 to 30 to 37 to 46 this year with two games remaining before the playoffs. He believes this team has a better chance to move past the first round after losing in seven games to the eventual champion Boston Celtics last year.
"This team is different from last year," Woodson said. "We had to fight just to get in and made a series out of the first round. This year is a lot different, and it started from day one. We are playing good ball."
The Hawks host Miami, which is fifth in the East and one game ahead of Philadelphia and two up on Chicago with three games remaining, in their regular-season home finale on Tuesday.
Atlanta improved to 30-10 at Philips Arena. The Pacers dropped to 11-30 on the road.
Johnson believes the Hawks, who are 14-24 away from Atlanta, still have a lot to learn.
"We can't relax even though we have home court," he said. "We have to figure it out on the road."
Hawks F Marvin Williams returned after missing the last 16 games with a lower back injury. "I hadn't run in a while. I took some early spills but I got back over it," Williams said after scoring five points in 12 minutes. ... Atlanta G Mario West started his first game of the season with F Maurice Evans out of town following the death of his grandmother. ... Hawks reserve C Zaza Pachulia didn't return for the second half because of a back injury. ... Indiana dropped to 2-19 when opponents shoot 50 percent or better. Atlanta hit 51.9 from the field.