Mann scored 16 points, including a go-ahead basket with 17 seconds remaining, and Georgia edged Mississippi 75-73 in the SEC tournament quarterfinals on Friday night.
Marshall Henderson scored 19 points for Ole Miss but made only 5 of 21 shots, including 2 of 16 3-pointers. Jarvis Summers led the Rebels with 26 points but missed a last-second jumper.
Georgia (19-12) will play Kentucky in the second SEC semifinal game on Saturday, following No. 1 Florida's game against Tennessee.
Ole Miss led 73-72 when Georgia's Kenny Gaines missed a 3-pointer, Brandon Morris missed a follow shot and Mann grabbed the rebound and scored on a layup to give Georgia the lead.
"It bounced my way and I just wanted to pick it up and attack the rim," Mann said.
Gaines and Morris each had 12 points for the Bulldogs, who may need to win the SEC tournament to earn a spot in the NCAA field. J.J. Frazier added 11 points.
There were 51 fouls called in the game. Sebastian Saiz and Dwight Coleby fouled out for Ole Miss (19-14).
Mann made two free throws to give Georgia a 72-71 lead. Summers answered with a jumper with 45 seconds remaining to give the lead back to the Rebels.
After Mann's go-ahead shot, Henderson missed a jumper and fouled Marcus Thornton, who made 1 of 2 free throws for a 75-73 lead.
Summers missed a last-second jumper following an Ole Miss timeout with 2.6 seconds remaining.
Henderson, emotional after the game, said his teammates encouraged him to keep shooting.
"They just said, 'Keep shooting, keep shooting. We'll live and die with it,'" Henderson said.
"It was hard. There are so many thoughts running through my head. It's crushing, in my heart, because I wanted it so bad for everyone. I take the blame for that. And that's what hurts."
Henderson set an SEC tournament record with 19 3-point attempts and scored 21 points in the Rebels' 78-66 win over Mississippi State on Thursday.
"Last night he made the big ones," Ole Miss coach Andy Kennedy said. "Tonight, the shots don't go. But we have to live with that because that's who we are."
The Rebels now will hope for a NIT bid.
"I think there's a chance," Kennedy said. "I would love to play in the NIT if we were given the opportunity."
Kentucky beat Georgia 79-54 in Lexington, Ky., on Jan. 25.
"They're good. They're terrific," Georgia coach Mark Fox said. "We're going to have to play super to win."
Georgia struggled with fouls in the first half. Thornton played only 5 minutes and Mann was limited to 7 minutes after each picked up two early fouls. Two more Georgia starters, Donte' Williams and Gaines, finished the half with two fouls.
Frazier, who took over for Mann, hit two 3-pointers and led Georgia with eight points in the half.
Ole Miss made only 1 of 11 3-pointers in the half. Henderson missed 6 of 7 3s, but Summers' scoring filled the void as the Rebels led 38-36 at halftime.
Fouls became a bigger problem for Ole Miss in the second half. Coleby fouled out with 8 minutes remaining, and Saiz drew his fifth with 3:38 remaining.
Fox was called for a technical foul when he disagreed with a foul called on Mann with 6:35 remaining. Fox continued to argue and pushed away assistant coach Jonas Hayes when Hayes tried to intervene.