The Miami Heat unleashed a barrage of three-pointers to score a series-levelling 111-101 upset over the top-seeded Boston Celtics in their NBA Eastern Conference playoff duel on Wednesday.

Eighth seeds Miami, playing without the injured Jimmy Butler, produced a battling performance to knot the best-of-seven-series at 1-1 as the teams head back to Florida for game three on Saturday.

Tyler Herro led the Miami scoring with 24 points, part of a balanced offensive effort that saw all five Heat starters post double-digit points.

But the key to the Miami victory was their accuracy from long-range, with the Heat draining 23 three-pointers from 43 attempts compared to Boston's 12 of 32.

Herro knocked down six threes while Caleb Martin added five in his tally of 21 points.

Boston, meanwhile, was led by 33 points from Jaylen Brown, with Jayson Tatum finishing with 28 in a losing effort.

The win was all the more unexpected given Miami's 20-point drubbing by Boston in game one on Sunday – something Herro said had motivated the Heat for game two.

"We lost badly in game one and everybody responded tonight, and that's that's all you can ask for from a group of guys," Herro said afterwards.

It was another trademark display of defiance from Miami, who are aiming to emulate their playoff run of last season when they reached the NBA Finals after entering the postseason via the play-in tournament.

"We don't even want to mention last year, this year is a whole new year," Herro said.

"We feel like we have a great group of guys. We're not fully healthy, but we have guys who want to play and want to be out here making a difference.

"This playoff opportunity is big for everybody. We just love to compete." (AFP)