Jayson Tatum and the Boston Celtics clearly are not ready to see the world that exists outside the NBA's restart bubble.

And a big second half extended their stay at Walt Disney World.

Tatum had 31 points and 10 rebounds, Jaylen Brown added 28 points and the Celtics staved off elimination by topping the Miami Heat 121-108 in Game 5 of the Eastern Conference finals.

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

Daniel Theis had 15 points and 13 rebounds for the Celtics, who trailed by 12 early but took control with a big third quarter. Kemba Walker scored 15 points, Marcus Smart added 12 and Gordon Hayward had 10 for the Celtics.

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

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 per cent on 3's in its last 13 quarters - after shooting 38.3 per cent in the playoffs before that drought.

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.

He turned a blew a kiss to the Heat bench after the second one, reminiscent of something Herro did during his 37-point barrage in Game 4.