BOSTON -- Both benches were being cleared. The Celtics, with an opening win in the bag, had a Thursday night date in Chicago on their minds. It was over.

But someone forgot to tell the Brooklyn Nets.

"We didn't end it like we wanted to, but we definitely got the win and that's all that matters," Isaiah Thomas said after the Celtics, ahead by 23 points in the fourth quarter and 21 with 5 1/2 minutes left, hung on for a 122-117 victory over Brooklyn that spoiled the head coaching debut of the Nets' Kenny Atkinson.

"If we want to be a top team like they say we're going to be, we have to do a better job of closing games out."

"That's the NBA for you," said Al Horford, who got a win in his first game with the Celtics. "I think it will humble you sometimes. We had a comfortable lead and we thought it was fine, but this is a good learning experience for our group.

"We have to keep playing the right way throughout 48 minutes."

And Atkinson, who has a roster with only five players who finished last season with the team, had to like what he saw.

"Very pleased that we didn't give up and we kept on fighting," he said. "I liked our grit in the fourth quarter."

Celtics coach Brad Stevens was forced to send his starters back in with 2:07 left and, even after that, the Nets had two chances to tie on the same possession -- Bojan Bogdanovich missing a pair of 3-pointers.

"It was 110-87 and we started shooting bad shots and not guarding and throwing it to the other team," said Stevens. "It's how quickly things can change; we all know that."

Thomas, who iced the game with a pair of free throws, led all scorers with 25 points, adding nine assists and six rebounds -- in a game that saw the Celtics chalk up 36 assists on 48 baskets. That's the most assists by a team in an NBA opener since 2001. They also had 19 turnovers.

"We could have even had more assists if we knocked down our open shots that we have," said Thomas.

Jae Crowder scored 21 points and Avery Bradley had 17 points, nine rebounds and five assists. Horford, signed to a big free agent contract over the summer, had 11 points, five rebounds and six assists in his Boston debut.

"I love playing with him," Bradley said of Horford.

Bogdanovich led the Nets with 21 points. Justin Hamilton came off the bench to score a career-high 19 points and match his career best with 10 rebounds. Jeremy Lin scored 18 points and Joe Harris 16.

Gerald Green, traded away from the Celtics in the 2007 Kevin Garnett-to-Boston deal, made his re-debut with Boston -- with his hair braided in an artistic shamrock on top of his head. He entered the game to a big hand in the first quarter and had nine points and five rebounds in 14 minutes.

Rookie Jaylen Brown, the third pick of the 2016 NBA draft -- a selection that came to Boston from Brooklyn in the Garnett/Paul Pierce deal -- played 19 minutes in his debut and scored nine points. He was welcomed by the crowd.

"It was wonderful, it was great, probably the best crowd in the world," he said.

Atkinson has been working with his new team on featuring 3-point shooting, and Brooklyn was 15-for-44 from behind the arc. Boston finished 11-for-32 from long distance, both teams at 34 percent.

"Yeah, 44 is a lot, but we'll look at them," said Atkinson. "We said we want to take them but they have to be open 3s."

Talking about Hamilton, who played 25:20 off the bench, Atrkinson said, "He's doing what he's done all preseason. I'm pleased with how he's fit with us."

NOTES: The Nets were without starting G Randy Foye (hamstring) and G/F Caris LeVert (foot, rehab) while the Celtics were missing G Marcus Smart (ankle) and F/C Kelly Olynyk (shoulder). Boston coach Brad Stevens said Olynyk, still recovering from surgery, is still a couple of weeks away from returning. ... C Al Horford received a rousing ovation from the crowd before his first regular-season game with the Celtics. He then excited the crowd by nailing a 3-point 1:23 into his debut. ... ESPN reported the Bulls had reached a deal with G R.J. Hunter, recently waived by the Celtics.... The Celtics visit the Bulls on Thursday night. The Nets play their home opener Friday night against the Indiana Pacers. ... Jordan Smith, the season nine winner of "The Voice," sang the national anthem. ... Patriots owner Robert Kraft and LeGarrette Blount were among those in the crowd.