BOSTON — Confidence is a hell of a drug.

Juiced by avoiding an Eastern Conference finals sweep in Miami, the Celtics overwhelmed the visiting Heat in a 110-97 victory that forced a Game 6 in South Florida that could have history waiting on the other side.

"Pressure's on them," Celtics star Jayson Tatum, who scored 12 of his 21 points in the first quarter and finished two rebounds shy of a triple-double, said in his walk-off interview. "We were down 3-0. No one thought we were going to win, so we're playing free and confident, and we're ready to go down to Miami."

On the first possession of Thursday's Game 5, Boston guard Marcus Smart stripped Miami center Bam Adebayo, dove for the loose ball and found Tatum streaking to a contested layup. Tone, set. An avalanche ensued. Playing their best basketball of the playoffs, the Celtics blitzed every possession on both ends, stormed to a 20-5 lead, amped it to 24 points and seeded doubt in the Heat for the first time in the series.

"Smart was just a beast tonight," said Boston's Jaylen Brown, coming off consecutive blowout wins.

"That was contagious," added Tatum. "Smart played his ass off tonight. Everybody did."

"I wanted to come in and give my team some energy early, especially playing against a team like Miami," said Smart, who swiped five of his team's 13 steals and scored 23 points on 12 shots. "You don't want them to come in and get that energy early without fighting back. This series has been that for us. They've come in each game and knocked us around a little bit early, and we did the knocking around tonight."

Must have been a wild Topgolf outing the Celtics enjoyed after falling down 0-3 to the eight seed. Once they quit in Game 3, it felt impossible that they could rediscover the identity that carried them to the 2022 NBA Finals in time to save this season and avoid questions about the future of their coach and roster.

That impossibility — becoming the first NBA team to come back from a 3-0 deficit — now feels plausible.

Reports began surfacing about dysfunction in Boston's locker room after the embarrassing start to the series, including one that suggested "this Celtics team feels like a group that’s tired of fake liking each other." Whether or not there is truth behind those reports, they seem to have galvanized their players.

"We've got a lot of love for each other, top to bottom," said Boston's Derrick White, who joined Tatum, Brown and Smart with more than 20 points in Game 5. "We're competing, and we know it's a long way to go, and we've got a lot of work to do, but it's always fun competing with the guys in our locker room."

"We didn't imagine being in this position, being down 3-0, but when adversity hits, you get to see what a team is really made of," said Brown. "It couldn't get any worse than being down 3-0, but we didn't look around, we didn't go in separate directions. We stayed together. We doubled down on what we're good at on defense, and now I think it's a series. We've just got to take it one game at a time and keep playing."

"We've got a really connected group," said Tatum, who feigned unfamiliarity with the reports. "We've got a group of determined, tough guys that I know I can count on. I know I'm going to look to my left and my right when all hope seems to be lost, when the game is on the line, our backs are against the wall, and everybody is going to go down fighting and give everything they have. That's contagious, because, whether it's ignorant belief, we truly do believe at all times that we still have a chance, that anything can happen."

Everything that went wrong for Boston in the first three games has gone right in the last two. Both the offense and defense flipped from performing at league-worst levels in the three losses (110.6 offensive rating and 124.4 defensive rating) to performing at league-best levels in the two wins (123.5 and 108.3). Some of that is a progression to the mean, but a lot of it is just the Celtics getting back to what they do.

(Or haven't been doing in the case of head coach Joe Mazzulla, who has started calling timely timeouts.)

Defensively, they are running Miami's shooters off the arc, no longer biting on every Jimmy Butler pump fake and trying to rip the ball from Adebayo every time he puts it on the floor. Offensively, they are driving, kicking and swinging into open 3-point looks (34-of-84 in Games 4 and 5); busting the zone by finding willing and able passers at the nail; and leveraging their size (32 second-chance points since Tuesday).

Brown's return to form as an All-NBA two-way talent on Thursday was another revelation. He shot 50% from the field for the first time since Game 5 of the second round and played lockdown defense, often opposite Butler, whose playoff-low 14 points showed his 33 years of age for the first time in the series.

Heat point guard Gabe Vincent's absence — along with injuries to Tyler Herro and Victor Oladipo — laid bare a lack of depth. Kyle Lowry started in Vincent's place and accepted blame for Miami's horrid start to Game 5. "I just wasn't aggressive enough," the 37-year-old said. The presence of Max Strus and Kevin Love in the starting unit presents too many weak spots to attack. Heat coach Erik Spoelstra abandoned Love in favor of journeyman Haywood Highsmith, who for a time was their leading scorer in the game.

The talent gap everyone anticipated all series is surfacing with each degree of increased confidence. In the third quarter alone, Al Horford gets Lowry on his back and spins into a dunk. Brown beats Strus baseline for another. Tatum rises over Strus from midrange. Walls are caving in on a Heat team that was once solid.

"One of our assistants put it in great perspective," said Mazzulla, whose Celtics have won their last seven elimination games in the East. "The seasons are nine months long, and we just had a bad week. Sometimes you have a bad week at work. We obviously didn't pick the best time to have a bad week, but we did, and we're sticking together and fighting like hell to keep it alive, and the guys are really coming together."

As Duncan Robinson — one of few bright spots for Miami in Game 5 — exited his postgame interview, someone in the hallway asked him if he had guaranteed the Heat would close out the series on Saturday.

"I'm going to leave that to Jimmy," he said.

Sure enough, Butler, who does not feel pressure — who embodies pressure — said, "We are always going to stay positive, knowing that we can and we will win this series. We'll just have to close it out at home."

Butler can only carry so much. The tide is turning, and Miami is at risk of succumbing to the undertow. In that same hallway, knowing smiles from Heat executives Pat Riley and Alonzo Mourning had faded from stunning Games 1 and 2 victories in Boston, replaced by gleeful smacks from Brown and Horford to Grant Williams' behind (each more ... enthusiastic than the last) during the Celtics forward's postgame interview.

"Who cares about mood?" said Spoelstra, rejecting the notion that his team's confidence is waning with each Boston waxing. "We have a gnarly group. I think so much of that is overrated. It's a competitive series. You always expect things to be challenging in the conference finals. One game doesn't lead to the next."

Tell that to Boston's home crowd, which, given one more chance to applaud a once-reeling favorite, arrived early, reached a deafening roar at tipoff and chanted "C's in seven" by night's end. Under no scenario do the Heat want to return to that environment with the weight of a 150-0 record for NBA teams leading 3-0 in a series filling the space between their tottering minds and those 17 championship banners in the rafters.

"It's a blessing to be able to play this game each and every night," said Brown. "It's a blessing to be in the playoffs. It's highs, it's lows, it's intense moments. There are moments where you're pissed off. There are moments when you're extremely excited. It's amazing. These next two games should be fun."

"It's not two games," corrected Smart. "It's one game for us."

And then back home, where everything is possible in a Game 7.