The Celtics welcomed back star pair Marcus Smart (24 points, nine rebounds, 12 assists) and Al Horford (10 points, three rebounds, three assists) and put in a comprehensive display after Miami won Game 1 following a third-quarter barrage.
Boston had won three of the four quarters in Game 1 but lost the third quarter 39-14 to eventually go down 118-107.
The momentum appears to be firmly with the Celtics in the series but Spoelstra reiterated it was only 1-1 in the Conference Finals.
“This only counts as one,” Spoelstra said. “That’s what the experienced players in the locker room and staff understand. We don’t like it.
“They played extremely well. You have two really good teams and we just have to figure some things out.”
Miami’s Jimmy Butler scored 41 points in Game 1 but had 29 points this time with six rebounds and three assists. He said the Heat were embarrassed the Celtics, who led 70-45 at half-time.
“It has to hurt,” Butler said. “They tried to embarrass us. They did embarrass us. Overall, we just have to be better.”
Jayson Tatum was excellent with 27 points, with five rebounds and five assists, including shooting four-of-six from beyond the arc.
Smart returned from a midfoot sprain with 24 points including five three-pointers while he added three steals too.
“I got to get my rest, got to get my health back, got to watch and see some things and come out and execute in this game,” Smart said.