Tyler Zeller had just enough time to catch Kendall Marshall's pass under the basket and put up a shot before the horn sounded.
The layup saved sixth-ranked North Carolina from a shocking exit from the Atlantic Coast Conference tournament.
Marshall penetrated into the lane and found Zeller for the buzzer-beating basket as the Tar Heels rallied from 19 down in the second half to beat Miami 61-59 in Friday's quarterfinals.
The top-seeded Tar Heels (25-6) spent most of the day playing nothing like the team that had lost just twice since December, including a rousing win against rival Duke less than a week earlier to clinch the regular-season title outright. They threw away passes against Miami's zone, couldn't establish their big men in the lane and couldn't get out in transition for easy baskets to build momentum.
Yet a frantic rally in the final 8 minutes sent North Carolina on to Saturday's semifinals against Clemson.
''We feel as lucky as we can possibly be,'' coach Roy Williams said. ''Those kinds of things happen in tournament time.''
It was North Carolina's biggest comeback since rallying from 20 down in the first half to beat Georgia Tech in 2006 and its biggest second-half comeback since rallying from 21 down against Florida State in 1993. It is also believed to be the program's biggest comeback in any ACC tournament game.
''That's the thing about this team: we just keep fighting and fighting,'' sophomore John Henson said. ''We came back good today, and that's what we do. I'm just glad we hit some shots.''
Zeller came through twice for the Tar Heels in the final minute, first scoring on a hook shot against Reggie Johnson to tie it at 59 with 45.3 seconds left. Then, after a Miami turnover, Marshall penetrated past Julian Gamble and drew Johnson away from Zeller.
Marshall's pass found Zeller almost directly under the basket, and he quickly put it up as Durand Scott rotated down from the foul line in a last-ditch attempt to block the shot.
''It's one of those things that people have made fun of me for not dunking, but it paid off on that possession,'' Zeller said. ''I just caught it, and I had to shoot it as fast as possible. I knew as soon as I let it go that I had gotten it off in time because I knew the buzzer had gone off after it was out of my hands.''
The officials had no doubts either, immediately signaling the basket was good to send the home-state crowd filled with plenty of light blue into a loud roar of delight.
The final play gave North Carolina its only lead of the game and left the ninth-seeded Hurricanes (19-14) to walk dejectedly off the court a day after staging their own improbable comeback, rallying from 10 down in the final minute to force overtime and beat Virginia in the first round.
While Zeller finished with 13 points, the Tar Heels managed just 14 points in the paint and had to rely on the outside shooting that had looked shaky for much of February. But Harrison Barnes (18 points) hit four of North Carolina's 10 3-pointers - with seven coming in the second half - while Leslie McDonald had 11 points and three 3s as part of a smaller lineup.
Compare that to the first half, when the Tar Heels were so bad that Williams subbed in five walk-ons for his top players at the 12:15 mark. They sat on the bench and quickly found themselves confronted by an angry Williams, who had dropped to one knee and launched into an angry and animated rant.
The tirade continued during a TV timeout less than a minute later, with Williams pointing at his players and pumping his fist before putting his starters back in at the 10:38 mark.
''I used my allotment of bad words for the month today,'' Williams said.
Meanwhile, the Hurricanes played with confident ease. They closed the first half on an 11-2 run to take a 31-22 lead at the break, then pushed the margin to 53-34 on Johnson's layup with 9:52 to play.
But the Tar Heels had a series of four 3s in a 2-minute span to cut a 16-point deficit to 55-51 with 5:13 left. Then, after Zeller tied it, Miami gave it back to the Tar Heels when Adrian Thomas couldn't handle a pass from Malcolm Grant and fumbled it out of bounds with 18.6 seconds left.
North Carolina shot 56 percent and had just six turnovers following the break after committing 14 in the first half, while Miami shot just 32 percent after halftime.
''We missed some wide-open shots and we took some ill-advised shots,'' Miami coach Frank Haith said. ''We just weren't taking good shots. ... We missed some bunnies around the hoop, and that was part of it. You've got to make those plays.''
Grant scored 16 points to lead the Hurricanes.
