Miami trailed by nine at the half before turning it around with a franchise playoff-record 46 points in the third and outscoring Boston 66-50 over the final two quarters. It was Butler's fifth game with 30 or more points this postseason and he added seven assists, six steals and five rebounds.
“One of the premier two-way basketball players of this association. ... That’s what we needed.” Heat coach Erik Spoelstra said. “Down the stretch Jimmy was able to do everything we needed – as a scorer and as a facilitator.”
Bam Adebayo added 20 points and eight rebounds. Kyle Lowry, Caleb Martin and Gabe Vincent and Max Strus all added 15 points apiece. The Heat went 16 of 31 from the 3-point line.
The No. 8-seeded Heat have opened all three playoff series with road victories. Game 2 is Friday in Boston.
Jayson Tatum led the Celtics with 30 points, but didn't take a shot in the fourth quarter. Jaylen Brown finished with 22 points and nine rebounds. Malcolm Brogdon added 19 points.
The Celtics, who are at their best when they're defending and getting up more shots than their opponents, were 10 of 29 from beyond the arc.
“We lost our offensive purpose,” Celtics coach Joe Mazzulla said.
Spoelstra said his team was “more intentional” over the final 24 minutes.
Miami took a page out of the Celtics' book and used a 13-1 run to quickly erase that gap and then nudged back in front in the third quarter, as Butler penetrated to create opportunities for his teammates.
The Heat outscored the Celtics 46-25 in the period and took a 103-91 lead into the fourth, prompting a few boos from the TD Garden crowd.
Boston responded, scoring the first seven points of the final period before a 3-pointer by Vincent ended the run.
Miami led 114-109 with just over three minutes to play when Brogdon was fouled by Butler. But he connected on just 1 of the 2 free throws. Butler was trapped on the next Miami possession before finding Martin for a corner 3.
Tatum travelled, giving the ball back to the Heat. A Miami miss gave the ball back to Boston, but Tatum was called again for travelling.
Miami wound the shot clock down before getting a 3-pointer by Butler to rattle in with 1:03 remaining.
