Tatum had 31 points and 10 rebounds, Jaylen Brown added 28 points and the Celtics shook off a slow first half to top the Miami Heat 121-108 in Game 5 of the Eastern Conference finals and stave off elimination.

“Our deal was to come out and play, come out and compete, give it our best shot and I thought we played pretty well in the second half,” Stevens said. “But we’re going to have to do it again and again because of the position we’re in.”

The Heat lead the series 3-2, with Game 6 on Sunday.

WATCH | Tatum leads Celtics past Heat in Game 5:

Daniel Theis had 15 points and 13 rebounds for the Celtics, who trailed by 12 early but outscored Miami 41-25 in the third quarter and never looked back. Kemba Walker scored 15 points, Marcus Smart had a 12-point, eight-rebound, eight-assist night and Gordon Hayward scored 10 for the Celtics.

Goran Dragic scored 23 points before fouling out with 4:27 left for Miami, which got 20 from Duncan Robinson.

“It’s certainly not going to be easy,” Robinson said. “We’ve got to band together to do difficult things.”

Jimmy Butler scored 17, Tyler Herro and Jae Crowder each had 14 and Bam Adebayo 13 for the Heat — which could get nothing to fall from 3-point range.

Miami was 7 for 36 from beyond the arc, now shooting 24.8% on 3’s in its last 13 quarters — after shooting 38.3% on those in the playoffs before that drought.

“Boston played great in that second half,” Heat coach Erik Spoelstra said. “They deserved and earned what they got. We understand how tough it is to win in the playoffs. We did not compete hard enough defensively and we paid the price for that. But you do have to credit Boston. They played with great force.”

‘You just want to give yourself a chance’

Brown made back-to-back 3’s in the fourth quarter to turn an eight-point lead into a 103-89 margin with 8:05 left, and things weren’t in doubt again. He turned a blew a kiss to the Heat bench after the second of those 3’s, reminiscent of something Herro did during his 37-point barrage in Game 4.

Game on. Series on.

“It’s not going to be perfect,” Tatum said. “You just want to give yourself a chance.”

The opening minutes didn’t go according to plan for Boston, which missed 11 of its first 12 shots, committed four turnovers in that dismal stretch to make matters even worse, and got into a 17-5 hole very early.

But they weathered all that and, even after shooting only 40% in the first half, Boston trailed 58-51 at the break — never leading, but never letting Miami get too far removed from view.

The Heat scored the first basket of the third quarter. The next few minutes were all Celtics.

They went on a 13-0 run over a stretch of only 3:06 to turn a nine-point deficit into a 64-60 lead, and the game changed just that fast. A separate 7-0 burst followed, Walker connected on a 3-pointer with 4:26 left for a 77-67 edge — Boston’s first double-digit cushion of the night.

“In all sincerity, first time I’ve seen Celtics basketball in the last few games,” Stevens told his team during a time-out.

And it was good enough to ensure that Friday wouldn’t be the last time he’d see Celtics basketball this season.