Smart had missed the opening game of the series through injury but returned with a vengeance in Game 2, racking up 24 points, 12 assists, nine rebounds and three steals in a 40-minute masterclass.
"I was pumped. I felt bad that I couldn't be out there with my teammates and go to battle with them," Smart told reporters after the game, speaking about his absence in Game 1.
"We're playing against a really good Miami Heat team. I got to get my rest, I got my health back, I got to watch and see some things and come out to execute this game."
The Celtics started the game slowly and had trailed 10-0 before Smart and his teammates got to work.
Jayson Tatum had 27 points, five rebounds and five assists in a solid overall performance while teammate Jaylen Brown added 24 points and eight rebounds.
Boston was also buoyed by the return of Al Horford who was deemed eligible to play just hours before the start after missing the first game due to the NBA's Covid-19 protocols.
'They did embarrass us'
Despite the loss, it was Miami's Jimmy Butler who led all scorers with 29 points and six rebounds but his game was stymied somewhat by the impressive Smart.
"I look at it as it can't get too much worse," Butler told reporters after the game. "They whipped our tail on our home floor.
"I guess if they do it on their home floor, it's supposed to happen, but I don't see us doing that again.
"They tried to embarrass us. They did embarrass us. So I think we got to realize that, use it as fuel, whatever you want to say, but realize the game can get out of hand when you're playing against a really good team like them that can score the ball and get stops.
"Overall, we have to be better. We have a tough job to do to go over there and win, but if they did it, we can do it, as well."
Boston is set to host Game 3 which is scheduled for Saturday.