ATLANTA (AP) -- On a night Miami lost its veteran leader, Atlanta again found new leadership from an unlikely veteran.
Anthony Johnson, pressed into starting duty by injuries to three other point guards, put up big numbers for the second straight game and the Hawks outlasted the Heat 117-111 in overtime on Wednesday night.
The Heat lost center Alonzo Mourning to torn patellar tendon in his right knee in the first quarter. He already has said he will not play next year, so the injury could end his career. A typical recovery period for the injury is three months.
"I think we should really wait on that," said Miami coach Pat Riley when asked about Mourning's chances for playing again this season. "But it's not good."
Johnson had a season-high 21 points and 9 assists, one game after he had 17 points and 14 assists in a win over Utah.
"A.J. has been phenomenal," said Hawks coach Mike Woodson. "He's running our ballclub, getting the ball where it has to go. He's defending for us and he's scoring. He's doing everything a point guard is supposed to do. It's beautiful to see, because I think guys are really starting to latch on around him, and they're playing right along with him."
The Hawks were without point guards Speedy Claxton, who has not played this season, and Tyronn Lue due to injuries. Rookie point guard Acie Law played only nine minutes in his return from an ankle injury.
Marvin Williams matched his career high with 26 points and had 10 rebounds. Joe Johnson also had 26 points with 9 assists for Atlanta (13-12), which has a winning record at the latest point since 1998-99, its last playoff season.
Miami, meanwhile, fell 11 games under .500 despite a season-high 36 points and 10 assists by Dwyane Wade, who made 20 of 22 free throws.
"Plain and simple, we couldn't get any stops," Miami coach Pat Riley said of the overtime, in which Atlanta outscored the Heat 13-7.
Joe Johnson gave Atlanta the lead for good with a three-point play with 1:05 left in overtime. The Heat have lost 8 of 11.
Wade's three-point play gave Miami a 111-108 lead in overtime. Johnson answered with a free throw and the three-point play.
Anthony Johnson added a running jumper with 14 seconds left to put the game away.
"We're all on a high right now, playing with a lot of confidence," said Joe Johnson.
A jam by Williams gave Atlanta a 97-89 lead with 5:45 left, but Udonis Haslem answered with a three-point play to start Miami's comeback.
Miami scored six straight points to cut the lead to 99-98, and a jumper by Wade tied the game at 100-all with 2:37 left.
With the game tied at 102, Wade blocked a shot by Horford with 1:17 left, and a jam by Haslem gave Miami a 104-102 lead. Joe Johnson tied the game at 104 with a short jumper. The teams traded turnovers before Ricky Davis missed a shot from the corner at the end of regulation.
Mourning was hurt when attempting to defend the basket on a layup by Atlanta's Mario West.
Replays showed Mourning's knee buckled as he was about to jump.
With Mourning laying on his back clutching his knee, a stretcher was brought to his side. Mourning was placed on the stretcher and then sat up, rose to his feet and limped to the Miami bench with the assistance of teammates.
The first postgame statistics showed O'Neal with only five fouls, prompting Riley to suggest he would protest the game. A review of the play-by-play sheet showed one of O'Neal's fouls was credited to Haslem, and the error was corrected. ... Miami point guard Jason Williams was held out with swelling in his left knee. ... Magic Johnson attended the game. ... Josh Smith fouled out with 1:43 left in regulation after scoring 12 points with five rebounds and four assists. ... The tie at the end of regulation was the ninth of the game.