In the end, his main man took over.
"It's winning time," Irving said after his latest heroics.
Playing without Jaylen Brown (swollen eye) and Marcus Morris (knee rehab), Boston won its fourth straight and improved to 22-4, 8-0 against the Western Conference and 2-0 against the Mavericks.
In both games against Dallas, the Celtics trailed by double digits. They improved to 7-3 when trailing in a game by at least 10 points this season.
Dallas blew a 13-point, fourth-quarter lead against the Celtics at home, then led by 10 at the half Wednesday and 12 early in the second half.
Irving continues to be special with the game on the line.
"He turned it on there late, but we didn't really make the runs that we should have when he wasn't out there," said Mavericks forward Dirk Nowitzki, who scored 16 points in what may have been his final game at TD Garden.
"With a great player, you try to mix it up, try to stay in front of him, try to make it tough on him. He made some tough shots in the fourth, made some runners, got to the basket a couple times with some nifty finishes -- that's what he's been doing all year."
Boston's Marcus Smart scored his only basket of the game to snap an 85-85 tie with 4:14 remaining and trigger an 8-0 run that broke it open.
Irving scored five straight points and then added another basket as the Celtics clinched their latest win with a 12-2 run down the stretch.
Al Horford, playing his usual all-around game, had 17 points, eight rebounds, eight assists, three blocks and two steals. Rookie Jayson Tatum also scored 17 and grabbed 10 rebounds. Terry Rozier had 12 points and a career-high nine rebounds, and Shane Larkin, coming off the bench after not playing for five straight games, scored 11 points in 15 minutes.
Daniel Theis grabbed 11 rebounds in 17 minutes for Boston.
"I'm very happy," Horford said. "Going into the season you never have any expectations. This is good. We want to keep building on it."
After the game, Horford called Rozier the best rebounding guard in the NBA.
Tatum is the first Celtics rookie with four straight 15-point games since Paul Pierce in 1999.
"Our first half was really good," Dallas coach Rick Carlisle. "Their second half was better, and that's the game and it's a 48-minute game. We've got to be able to sustain."
The Celtics recorded 25 assists on 36 baskets.
Without Brown, who woke up with a swollen eye, and Morris, who has been so effective coming off the bench in recent games, the Celtics were missing 27.4 points and 13.6 rebounds per game, causing Stevens to go deep into his bench. He employed Larkin, Guerschon Yabusele (three points, three assists and two rebounds in 6:35) and Abdel Nader (three points in 7:01).
"We mentioned that at shoot-around that everybody has to be ready, especially when we call to the bench," Rozier said. "You've got to have that 'next man up.'
"Just covering for one another. We're a team. We're pros for a reason. You put all that hard work in and you have to be ready."
Nowitzki, who may or may not play his 20th season in 2018-19, received a warm ovation pregame and said he hopes to play in Boston again. He and the rest of his team had all kinds of trouble down the stretch, scoring five points in the final 4:14 including a meaningless Wesley Matthews 3-pointer at the buzzer.
NOTES: Dallas G Devin Harris left the game in the second half with what looked like a left hand injury. ... The Mavericks announced C Nerlens Noel, who had a homecoming on this trip, will fly to Cleveland on Thursday and have thumb surgery for a torn ligament near his left thumb Friday. He could be back as soon as mid-January. ... Dallas G J.J. Barea, a Northeastern Huskies alum, visited his old campus Wednesday to raise money for Paws for Puerto Rico fundraising effort as he continues to try to help his devastated homeland. ... The Mavs continue their three-game road trip at Milwaukee on Friday, while the Celtics start a three-game trip in San Antonio the same night.