Johnson scored 23 points and came up with a huge offensive rebound, leading Atlanta to an 84-81 victory in Game 6 on Thursday night, knocking the Orlando Magic out of the playoffs.
The Hawks, who won the series 4-2, advanced to the second round for the third consecutive year, this time against top- seeded Chicago. Game 1 is Monday night.
Orlando, which routed Atlanta a year ago in the most lopsided four-game sweep in NBA history, heads into an uncertain off-season after its earliest playoff ouster since 2007.
With Atlanta clinging to a one-point lead and the clock running down, Marvin Williams missed a clinching 3-pointer. But Johnson swatted the rebound to Jamal Crawford, who was fouled and made both free throws with 8.2 seconds left.
"I just wanted to make a play," said Johnson, who bounced back from a dismal 5-point effort in Game 5. "The play was a pick-and-roll for Al (Horford) and Jamal, but we didn't come up with what we wanted. I just crashed the glass and tried to somehow get a hand on it. I did."
The Magic had two chances to force overtime. J.J. Redick missed an open 3, then Jason Richardson had a desperation shot from the corner blocked by Josh Smith.
Dwight Howard led the Magic with 25 points and 15 rebounds.
Crawford scored 19 points for Atlanta.