Mazzulla said he may have been trying to account for too much as he prepared his team for Friday’s game against the Heat. He believed it would have been smarter to distill the message, at least for now.

And that, he said, was to blame for Boston’s sordid start in which it made just 1 of 21 3-pointers.

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“I think you can over-prepare,” he said. “I think you can overthink. I think you can just get to a point where, ‘OK, we acquired somebody new, here’s all the possibilities we could get to.’ We may see five of those tonight, instead of just focusing on one or two.”

Still, the horrendous shooting led to a 22-point deficit that was significant but not impossible to overcome. 

Midway through the third quarter, their 3-pointers started falling and Vucevic started looking more comfortable, all while a previously sleepy Garden crowd was recharged with playoff-like energy.

The final result was a surprising 98-96 win that was secured when Heat guard Davion Mitchell missed a 3-pointer from the left corner in the final seconds.

Mazzulla said that the early deficit was not a fair indicator of how the team was playing, and that it was helpful to grasp that.

“I thought the guys did a great job having an understanding of, this is the truth, and then this is how it feels,” he said. “And then how do we stick to the truth? And then how do we keep chipping away? And then it was 21, and then we got it down to 12, and then it was 7, and the next thing you know, we’re up 2.”

The Celtics, who have won five games in a row, trailed by 18 with seven minutes left in the third quarter. But they erased the rest of that deficit by the start of the fourth and had no intention of wasting that effort.

Jaylen Brown had 29 points and Payton Pritchard scored 19 of his 24 in the second half. Vucevic, who received a warm ovation when he entered the game in the first quarter, had 11 points and 12 rebounds in his Celtics debut.

“I felt pretty comfortable out there,” Vucevic said. “I think as the game went on, I think that the guys also felt more comfortable around me and were able to figure out certain things that they want us to run. I think for the first game, it was good.”

Andrew Wiggins had 26 points to lead the Heat, who also coughed up a 19-point lead in a loss to the Celtics last month. 

Boston closed the game by making 9 of 15 3-pointers, turning its grisly beginning into a footnote.

“It’s kind of crazy to shoot 1 for 21,” Derrick White said, “but I was like, ‘We’re still only down 17.’ It felt like we were down 30 or 40. So just keep continuing to trust the process and you make one and the flood gates kind of open.”

Payton Pritchard makes a 3-pointer over Miami’s Simone Fontecchio during the third quarter.Matthew J. Lee/Globe Staff

The Celtics pushed back into contention with a 12-0 third-quarter run that was sparked by Pritchard and led, 79-74, early in the fourth.

A Wiggins 3-pointer put the Heat back in front, 94-91, with 3:58 left before Brown came up with a steal in the backcourt and scored.

With Boston trailing by 1, Brown won a critical jump ball against Heat big man Bam Adebayo, leading to a White 3-pointer from the right corner that gave Boston a 98-96 lead.

After Brown was whistled for an offensive foul with 40.9 seconds left, White stepped forward and swatted away a Mitchell layup attempt to preserve the lead. He missed a 3-pointer on Boston’s next possession, giving the Heat a final chance.

Wiggins attacked the rim and found Mitchell in the left corner for a clean, open look. But the shot caromed off the rim, and Boston’s comeback was complete.

“That’s a good sign when, even in the midst of figuring stuff out or not playing well, you find a way to win,” Brown said. “So, I’ll take the win over everything.”

Governor Healey joins Ben Volin live from Radio Row in San Francisco ahead of Super Bowl LX. The governor discussed how much this Patriots team is loved.

Adam Himmelsbach can be reached at adam.himmelsbach@globe.com. Follow him @adamhimmelsbach.