BOSTON -- Celtics coach Brad Stevens has seen Isaiah Thomas do some pretty special things on the basketball court.

None could have been any more special than what the little big man did for Boston on Wednesday night.

"He's got a knack for it," Stevens said after Thomas erupted for 20 points over the final 6:01 to lead Boston to a 90-83 victory over the undermanned Dallas Mavericks. "I guess I'm so used to being around him, so used to watching him operate that nothing surprises me."

Taking advantage of injuries to the Dallas backcourt, Thomas put on a one-man show, scoring 22 in the quarter to finish with 30 -- and assisting on one of the two baskets he didn't score down the stretch with a dynamic behind-the-back pass to Avery Bradley.

With Deron Williams, J.J. Barea and Devin Harris all out with injuries by game's end, Thomas, who hasn't scored fewer than 23 points in a game this season, took over. He was 3-for-13 from the floor through three quarters before breaking loose. Thomas finished with six assists and four rebounds.

Asked what happened in the fourth quarter, Thomas said, "I couldn't tell you ... I guess I just like that quarter. Sometimes guys get a little tighter and the pressure gets a little tougher for them, and I guess I like the pressure."

With no real guards to cover him, Thomas fouled 7-footer Andrew Bogut out with a 3-point attempt (he hit the three free throws) and then drove past 6-11 Dwight Powell on the next two possession.

Thomas heard chants of "M-V-P" as he sank two free throws with 41.4 seconds left.

Bradley, who finished with 18 points and a career-high 13 rebounds, scored on a flying slam dunk off that Thomas feed.

Bradley's rebounding helped the Celtics, normally rebounding challenged, to a 40-27 boards advantage -- their highest differential in two seasons.

"I'm not ready to anoint us the greatest rebounding team in the world yet," Stevens quipped.

Harrison Barnes and Wesley Matthews did their best to keep the Mavericks alive, but with Dirk Nowitzki on the bench in street clothes and the guards hurt, Dallas (2-8) just ran out of gas. Barnes, who signed a $94 million contract with the Mavs after leaving the Golden State Warriors as a free agent, hit tough jumper after tough jumper en route to 28 points. Matthews had 22.

"There's no real secret. We're going through some adversity right now," Barnes said. "We've just got to keep fighting. We're putting ourselves in position to win."

Kelly Olynyk was the only other double-figure scorer for the Celtics, with 10 points.

Williams, who returned to the Dallas lineup after missing four games with a calf injury, logged 9:34 in the first half, didn't score, missed all three shots, two from 3-point range, then left the game and didn't return.

Barea, who had been starting in place of Williams, went to the floor in pain with a left leg injury in the fourth quarter and was helped from the floor. He had nine points and six assists in 28 minutes off the bench.

"It was awful -- I've never felt that before in my career," said Barea, who played his college ball at Northeastern in Boston. "I thought it was the Achilles. A little bit of good news, it's my calf. Hopefully I don't need surgery or anything and just have to wait. I've never felt that feeling before."

He left in a walking boot.

There were no free throws in the second quarter, with Dallas taking just one in the half -- and that one was on a technical foul on a defensive three-second call. The Celtics (6-5) were 2-for-6 from the line in the half. The two teams that had gone to the line the fewest times in the league combined for seven attempts before the break.

Dallas didn't take its first lead of the game until there was 8:14 left -- and the Mavs actually led by four with 6:16 remaining.

Thomas, who also had five of Boston's 19 turnovers, then took over, starting his run with a 3-pointer.

"He's done it so many times ... certainly Isaiah's fourth quarter was tremendous," Stevens said.

NOTES: F Dirk Nowitzki (Achilles) and G Devin Harris (toe) remained out for the Mavericks. On Nowitzki, who missed his fifth straight game, coach Rick Carlisle said: "He worked out this morning hard. He's getting closer, but he's not there yet." ... The Celtics were still missing F Al Horford (concussion) and F Jae Crowder (ankle), but both should be close to a return, with Crowder expected to practice Thursday. Coach Brad Stevens said both players had "a great workout" earlier Wednesday. ... The Mavericks host the Memphis Grizzlies on Friday. The Celtics complete their two-game homestand against the Golden State Warriors on Friday before they depart on a three-game road trip.