Derrick White converted an offensive rebound in the last split second and Boston won 104-103 in Miami, which means the Heat and the Celtics will have an ultimate matchup in the Eastern Finals.
There were three seconds on the clock when White brought in Marcus Smart, whose long shot just missed. White had time to sneak into the right spot just in time to sign the key basket.
The Heat and their fans were waiting for the signal to really gloat after three free throws from Jimmy Butler in the moments before, for a 103-102 Miami lead.
It is therefore Monday at TD Garden that we will find out who will face the Denver Nuggets in the NBA Finals. The final round will begin on Thursday.
Only four clubs, including this edition of the Celtics, have erased a 3-0 deficit in a best-of-7 series and forced a seventh game.
In 150 occasions, the club climbing the slope has never managed to advance on the board.
Jayson Tatum had 31 points, five more than Jaylen Brown. Smart added 21 points, 10 more than White.
Note also the ten points of Robert Williams.
Boston won despite a 20% night on three-point shooting (seven for 35).
At the Heat, Butler scored 24 points, Caleb Martin 21.
Duncan Robinson had 13 points, but with 53 seconds left he missed a long-range shot that would have put the Heat up 103-101 on the heels of a successful block by Bam Adebayo.
The Heat fell despite a brilliant touch in general for three-point shots, with a success rate of 46.7% (14 for 30).