Smart, sidelined since Nov. 20 because of a knee injury, finished with six points on 2-of-6 shooting with three rebounds and an assist.
He was minus-6 in plus/minus, but the Celtics are excited about having their defensive pest back.
"Marcus is always a ball of energy," said Evan Turner, who shared ball-handling responsibilities with Smart on Boston's second unit on Sunday. "I think he played well [Sunday] for not playing live or practicing for a while. It's great to have him back. He made some big shots, especially that 3 in the fourth quarter. It helped a lot."
Smart drew cheers when he checked in for the first time late in the first quarter. He got burned on a Knicks give-and-go early in his first shift, but responded with a little and-one floater on Boston's ensuing possession.
Smart looked smooth hitting a fourth-quarter 3-pointer, but coach Brad Stevens didn't lean too heavy on him during his first game back.
"I thought he was good," Stevens said. "He played those two six-minute stints; I thought he did pretty well. And gave us a nice lift."
Smart, who was the team's starting point guard before getting injured, has pledged to help the team in whatever role he's asked, especially while working back to game shape. He wasn't full-throttle Smart in his first game back, but he tried to impact the game in his limited floor time.
"I felt pretty good," Smart said. "I did a very good job warming up the body. Getting out there felt good to play with those guys again."
Asked what he was able to contribute, Smart said, "Just hustle plays, especially being my first game back, just trying to bring the energy back to the team."
Isaiah Thomas, who has ascended to the starting point guard role in Smart's absence, said he liked what he saw of Smart.
"[Smart] looked good," Thomas said. "He hit a few shots. He played the usual defense that he plays. And I was surprised how good he was moving. I can't wait until he's back full force."
Added Thomas: "He's a hell of a player that brings so much energy. ... You know you're going to get energy and a guy who is going to defend. And then when he's playing well on offense, that's a cherry on top. Once he gets back in this groove, we're going to be an even more complete team, and I can't wait until that day comes."
Stevens said before Sunday's game that the Celtics felt comfortable throwing Smart back into the fire despite the lack of activity since being cleared to return.
"Here's the deal: Is it better to practice him and hold out until your next practice is scheduled? It just doesn't allow for very many of those," Stevens said. "And even when you do, you don't go very hard up and down. That's nine other guys that have to do something when maybe it's not best for your team to do that. So he's just going to have to play and get some of that through playing, and he's going to have to impact the team the best way that he can by defending, by being tough and by being an energy player for the time being."
The Celtics went 10-8 during Smart's absence. Asked if he would eventually like to resume his starting role, Smart said that isn't up to him and that he's OK coming off the bench if the starting combo of Thomas and Avery Bradley continues to perform at a high level.
"Those guys have been playing very well with Isaiah and Avery in the starting lineup, so I don't want to mess anything up," Smart said. "Keep the rhythm going, and, if it means I have to come off the bench for this team to keep winning games, then I'll come off the bench."
A second-year guard, Smart was averaging 9.8 points, 3.8 rebounds, 3.2 assists, and 1.8 steals over 29.1 minutes per game in nine appearances as the team's starting point guard before the injury.
Smart said before Sunday's game that he knows not to expect too much too quickly.
"I'm going to be a little rusty out there, so I'm just going to try to take it slow and kind of get back in the groove of things," he said.
Pressed whether it's even possible for him to take things slow, he said, "I kind of have to now. My body can't, even though I'm used to playing at one speed, this is an important time for me to just kind of gradually gain my confidence back on the floor and trust in my body again."