Miami, Florida - The Celtics needed just one stop to force a previously unthinkable Game 7 in the NBA's Eastern Conference finals.

They didn’t get it, then still did it under even more unthinkable circumstances.

The Celtics’ season suddenly looked lost, taken away from them in an instant. Leading by two in the dying seconds, they suffered from an unfathomable sequence. Al Horford fouled Jimmy Butler. Celtics coach Joe Mazzulla challenged the call. The foul was upheld, but Butler was given three shots, ruled behind the 3-point line. He sunk all three shots.

Then, needing a miracle, the Celtics pulled it off.

NBA New York Liberty receives hero's welcome with ticker-tape parade for WNBA title!

Marcus Smart’s shot was no good, but Derrick White crashed the glass and tipped it in. Somehow, it came before the buzzer sounded. The Celtics escaped. When it was official, they erupted into celebration on the court at Kaseya Center.

Celtics 104, Heat 103. Unbelievable.

After falling behind 0-3 in these Eastern Conference finals, the Celtics have stormed back. They won three consecutive games, the last one in epic fashion. There will be a Game 7 on Monday night in Boston, where the C’s will look to become the first team in NBA history to overcome an 0-3 deficit and advance to their second consecutive NBA Finals. Unbelievable.

Celtics fans erupted in celebration in Boston, seen in video footage blocking streets of traffic and climbing street signs.

The Celtics led by double digits on two separate occasions in this game, including by 13 with 3:27 to go in the third quarter. Despite their poor outside shooting, and Jayson Tatum (31 points, 12 rebounds) going absent for stretches, the C's looked like they would pull away.

But turnovers mounted for the C's in addition to missed shots, and the Heat mounted a comeback. Miami went on an 18-4 surge and an 11-3 run early in the fourth. The Heat pulled ahead by one on Butler’s tip layup.

But then one play changed the momentum. On the Celtics’ next possession, Brown was fouled and Bam Adebayo was whistled for goaltending the basket while hanging on the rim, which warranted a technical foul. Brown made both free throws as the C's finished a four-point possession.

NBA WNBA Finals: Breanna Stewart leads Liberty past Lynx in thrilling Game 2

Duncan Robinson scored five consecutive points to cut Boston’s deficit to four. But then Derrick White hit a huge 3-pointer and after another stop, Marcus Smart finished an impressive three-point play as he crashed to the floor to give the Celtics a 10-point lead.

Moments later, "Let’s go Celtics!" chants filled the air inside the Kaseya Center. The Celtics sensed victory, but finishing it off was never going to be easy. Not against the Heat.

The Celtics led by nine with 3:04 to play. Butler (24 points, 11 rebounds, eight assists), mired in an awful night, willed them back, scoring five consecutive points to bring them back. A year after his 3-pointer fell short in Game 7 that would have sent the Heat to the NBA Finals, it looked like he had redeemed himself.

Until White had other plans.

Other takeaways:

For most of the season, the Celtics have been a team that lives and dies by the 3-pointer. But they jumped out to a big lead in the second quarter because they were elite in the mid-range and outscoring the Heat in the paint.

The Celtics made only three 3-pointers in the first on just 15 attempts — both well below what they prefer — and didn’t have a single make from deep in the second quarter. But Tatum got hot from the mid-range and was getting whatever he wanted on drives to the basket and went to the free-throw line 11 times in the first half.

Tatum scored 25 points in the first half, including 16 in the second quarter as he took over. His lob to Robert Williams — who flushed home a one-handed alley-oop — and then layup put the C’s up 52-41 with 4:15 remaining in the first half. But the Celtics didn’t close the half well. They didn’t make any field goals over the final 3:41 of the second as the Heat put together a 12-5 run that cut Boston’s halftime lead to four.

Brown started hot, making his first five shot attempts — including three tough mid-range jumpers — that staked the Celtics an early lead. But he didn’t quite look the same after being fouled under the basket early in the second. He favored his ailing wrist after the foul and seemed to be upset by the contact. He proceeded to make just one of two at the line before committing a pair of turnovers, and picked up his third foul on a charge with 2:43 left in the first half.

Brown may have gotten away with a fourth foul in the opening minute of the second half. The Celtics star initially scored on a three-point play even though it looked like he hooked his arm around Caleb Martin (21 points, 15 rebounds) to get the bucket. Heat coach Erik Spoelstra challenged the call and it was successful, but it was deemed to be no foul at all on the play. Brown’s bucket still counted.

But about a minute later, Brown picked up his fourth anyway as the Celtics committed four fouls and went into the penalty in the first 2:48 of the third.

The Heat only went 9 for 23 from 3-point range in Game 5, and it seemed to be a clear priority to increase those numbers in Game 6. The Celtics consistently lost shooters — including, somehow, Martin, who continued to torch them in this series — as the Heat went 9 for 15 from deep in the first half. That included three from Gabe Vincent, who returned after missing Game 5.

The Celtics, however, did a fine job defensively on Butler in the first half. They held the Heat star to just nine points in the first half and 5-for-21 shooting for the game.

Game 7 of Celtics vs. Heat will tipoff on Monday, May 29 at 8:30 PM EST in Boston. The winner will head to Game 1 of the NBA Finals on Thursday, June 1.