Isaiah Thomas sat on a chair at his locker after the Celtics’ 90-83 win over the Mavericks and looked exhausted as he scrolled through his phone. He had yet to shower, and his knees were wrapped in ice. His entire left hand was wrapped up and iced, too, as the bandage looked like a boxing glove covering the middle finger he sprained on Saturday.

The Celtics’ massage therapist, Vladimir Shulman, came into the locker room and asked Thomas if he needed his assistance, which Thomas often does after physical games like this one. But since the Celtics will not practice on Friday, he waved off Shulman and told him he would send him a text message in the morning.

Thomas is a whirling, swirling 5-foot-9-inch menace, and the only way he knows how to play causes his body to take an incessant pounding. It is that way often, and it certainly was that way in the fourth quarter on Wednesday night.

The Celtics, coming off a disheartening loss to the lowly Pelicans on Monday, were back home to face yet another struggling team, the two-win Mavericks. Yet as the midway point of the fourth quarter approached, Dallas had improbably come back from a 12-point deficit to take a 4-point lead.

The Celtics needed someone, and when that is the case, they usually turn to Thomas. The point guard erupted for 20 points in the final 5 minutes, 58 seconds of the fourth quarter, sending his team to a much-needed win prior to the Warriors’ arrival here on Friday.

“I guess I just like that quarter, man,’’ Thomas said. “Sometimes guys get a little tired and the pressure gets a little tougher for them. I guess I like the pressure.’’

Thomas finished with 30 points, 6 assists and 4 rebounds. Through the first three quarters he went 3 for 13 from the field and 1 for 3 from the foul line. His shots were short and he was out of rhythm, partly because of the sprained finger on his shooting hand.

But in the fourth quarter he was 4 for 5 from the field and 12 for 13 from the foul line.

“You could see the lift and the rhythm that he had into a couple of them,’’ Celtics coach Brad Stevens said. “He was unbelievable.’’

With 6:15 left, a 3-pointer by Wesley Matthews gave the Mavericks their largest lead of the game, 70-66. The fans here became uneasy, but Thomas did not.

He hit one 3-pointer, and was fouled on another. He attacked the basket for a layup and even drew a foul when he went for a rebound against 6-10 center Dwight Powell. Thomas tallied 13 consecutive Celtics points over a stretch of 2 minutes, 55 seconds to give Boston a 79-76 lead.

After a high-arcing 3-pointer by Thomas made it 84-79 with 1:31 left, the he rebounded a Matthews miss and fired an outlet pass to Avery Bradley for a dunk that all but put the game away.

“I just feel like I’m on a little different level right now, and that goes with the confidence my guys give me,’’ Thomas said. “Like I always say, I’ve always been ready to take advantage of my opportunity, and my opportunity is here to try to be great. And I want to be great.’’

The Celtics’ primary deficiency this season has been their rebounding, and for one night at least, they were the team gobbling up missed shots. In all, they outrebounded the Mavericks, 53-32, and surrendered just five offensive rebounds, despite once again playing without injured starting forwards Jae Crowder and Al Horford.

Bradley continued to be a revelation as the team’s most unlikely rebounding force. The 6-2 shooting guard grabbed a career-high 13 caroms to go with 18 points. Bradley, who has never averaged more than 3.8 rebounds in a season, already has six double-digit rebound games this year.

“That’s just something I know our team needs,’’ Bradley said, “and I’m here to do whatever I need to do to help our team, wherever it is.’’

At the start, the Celtics were crisp and precise. They made their first five field goals and they were attacking on fast breaks and firing perfect outlet passes.

Late in the opening quarter, rookie forward Jaylen Brown streaked in for a one-handed dunk and then converted a difficult fadeaway in the post, giving Boston a 29-17 lead.

The Celtics made 12 of their first 21 shots before their offense stalled.

Boston was fortunate that the Mavericks were not very effective in the second quarter, either. Despite the fact the Celtics missed 17 of 22 shots, committed five turnovers and did not attempt a free throw, they were outscored just 14-10.

With 10:54 left in the fourth the Mavericks took their first lead, 57-56, when Justin Anderson threw down an alley-oop dunk.

Dallas trailed by a point with 7:37 remaining when point guard J.J. Barea took a bad step and crumpled to the floor.

He smacked the hardwood several times and was surrounded by players from both teams before he was helped to the locker room.

He said after the game he believes the injury was to his calf muscle and not his Achilles’.

Prior to getting hurt, he was helping pester Thomas. After he left, Thomas could not be stopped.

Adam Himmelsbach can be reached at adam.himmelsbach@globe.com. Follow him on Twitter @adamhimmelsbach.