The senior hit the go-ahead 3-pointer with 13.1 seconds left, helping the Bruins beat the Tar Heels 83-80 on Sunday in the Hall of Fame Tipoff.
Mann finished with a career-best 28 points, with the last basket giving the Bruins an 81-80 lead. Then, after a missed shot from UNC's J.P. Tokoto, Caleb Chowbay scored on a breakaway layup with 0.2 seconds left that sent Belmont players rushing onto the court to celebrate at the horn.
"There aren't great victories unless you beat great programs," longtime Belmont coach Rick Byrd said. "... It's a big moment right now for us."
Indeed, especially considering it appeared the Bruins (3-1) would be left lamenting one that got away.
Belmont had frustrated North Carolina by playing with poise and knocking down outside shots, leading by 11 points early in the second half. Then the Tar Heels (2-1) rallied and led by eight with 2½ minutes left, only to see Mann and the Bruins push back.
With the Bruins trailing by two in the final 20 seconds, Reece Chamberlain brought the ball upcourt and flipped it to Mann, who launched the straightaway shot over Tokoto.
He said he was "about 99 percent sure it was going in" before it dropped through the net.
"It's something you dream about as a kid, and something that you pretend this summer in the gym," Mann said. "You're saying, 'All right, game winner against North Carolina, here you go.' And then it happens. It's just unbelievable."
Belmont is a consistently successful Ohio Valley Conference program with six NCAA tournament trips in eight years. Now the Bruins have their first win against a Top 25 opponent since beating No. 23 Missouri in December 2003.
It was North Carolina's first nonconference home loss since falling to Illinois in the ACC/Big Ten Challenge eight years ago.
Drew Windler, who rebounded Tokoto's late miss and threw it ahead for Chowbray's layup, said he had 28 congratulatory text messages and countless other Twitter messages waiting by the time he got on the team bus.
"It's a historical win for Belmont," Windler said. "We don't have a lot of wins over AP Top 25 teams. So anytime you can go into a Top 25 team's place, especially a place like North Carolina — storied program — and do just enough to beat a good team, that's great. That's something to hang your hats on."
Mann hit five 3-pointers and added nine rebounds to lead the Bruins, who hit 15 of 37 3s to match their three-game season total for made 3-pointers coming in.
Windler scored 16 points and hit four 3s of his own for the Bruins, who shot 45 percent and hit 20 of 22 free throws.
The free throws were a big factor considering the Tar Heels — playing yet again without leading scorer P.J. Hairston and senior guard Leslie McDonald due to NCAA eligibility concerns — couldn't make their own.
UNC shot 48 percent and scored 20 second-chance points, but finished 22-for-48 (46 percent) from the foul line. That included a woeful 9-for-28 in the first half as Belmont took a 41-34 lead at the break.
"I don't know," sophomore Brice Johnson said of the free-throw struggles. "That hurt. We should've made free throws. ... Make at least 10 of those we win the game. We just have to concentrate, just take our time."
North Carolina erased the deficit with a 14-0 second-half run, holding the Bruins to one field goal over a 10-minute span. But after the Tar Heels had pushed ahead 73-65 on Marcus Paige's driving basket with 3:46 left, Mann and the Bruins pushed back.
Mann knocked down a 3 to cut the deficit to 78-75 with 1:02 left, then followed with another 8 seconds later to cut the deficit to 80-78.
The Tar Heels had a chance to make it a two-possession game again, but Paige lost the ball on a dribble drive with 19.9 seconds left, leading to a jump ball that set up Mann's final shot.
James Michael McAdoo scored a career-high 27 points and had 13 rebounds to lead the Tar Heels, while Paige finished with 17 points.
"(Byrd) is a good friend and a really good coach, and I'm happy for him," UNC coach Roy Williams said. "But I love those kids in my locker room and their coach let them down today. That's about it."