Rozier scored the last eight Boston points of the first quarter to give the Celtics an 11-point lead, and had another eight in a row midway through the fourth when they expanded the lead to 21. Marcus Smart and Jayson Tatum had 15 points apiece, and Irving and Al Horford each had 11 points and nine rebounds to help Boston to its fourth straight win.

James had 19 points, seven rebounds and six assists, and Tristan Thompson had 10 points and 10 rebounds for Cleveland, which lost for the fourth time in five games. Playing on back-to-back nights – the Celtics had been preparing for them since New Year’s Eve – Cleveland shot 34.8 percent.

It was the first time the teams had played since the season opener, when top Boston free-agent Gordon Hayward broke his leg and in a gruesome injury that reshuffled the Eastern Conference playoff race. The Celtics finished with the top seed last year, but lost in the conference finals to Cleveland.

And so much has happened since then.

Thomas was traded for Irving, then missed the first 36 games of the season with a hip injury before making his season debut on Tuesday night. In that time, he stewed over his departure from Boston, where he developed into an All-Star and fan favorite.

The Celtics scored seven straight points midway through the first quarter to turn a one-point deficit into a 15-9 lead. They ran off the last five points of the quarter – all by Rozier – on a tip-in and a 27-foot 3-pointer just before the buzzer that made it 32-21.

WELCOME HOME

Thomas made his first appearance at the new Boston Garden since the trade, but he did not play. Although he had expressed shock at the trade and held a grudge toward Danny Ainge, who orchestrated it, the relationship between him and the Boston fans remains unblemished. (Thomas also said on Wednesday that he had mended fences with Ainge .)

Thomas, who asked the Celtics not to play a video tribute, saying he would prefer to be honored when he was actually playing, got a cheer from the crowd when he joined his teammates on the bench late in the first quarter and made a brief appearance on the video board.

At the break, cameras again showed Thomas. And this time, the crowd rose to its feet for a standing ovation. The Cavs guard pounded his heart three times, smiled and gave a little wave before returning to his seat for the start of the second quarter.

HAPPY TO BE BACK

Thomas said he has a long way to go before he feels like himself on the court. But after his seven-month absence, he said playing Tuesday night against Portland was one of the most special moments of his career.

”There’s still movements that I’m scared to do. But it’s just because I’ve been out for so long,” he said. ”For the most part when you get hurt the mental part is the toughest part. My wind isn’t there. I’m not in that good of a shape. Obviously my game isn’t where I want it to be, but it showed a positive step in the right direction that I’m not far where I want to be.”

TIP-INS

Cavaliers: Kevin Love left the game early in the fourth quarter with a right ankle sprain. He finished with two points and five rebounds in 21, going 1-for-11 from the floor and missing all four 3-point attempts.. … Jae Crowder also made his first trip to Boston as a visiting player. He finished with six points and nine rebound son 2-for-12 shooting. … The Cavaliers are 14-4 over the last 18 matchups against Boston, including two playoff series.

Celtics: Seen in the crowd: Gymnast Aly Raisman, Red Sox manager Alex Cora, Red Sox outfielder Mookie Betts, Patriots Dion Lewis and James White and former Patriot Troy Brown. … Aron Baynes limped to the locker room in the second quarter but returned. He finished with six points. … Irving hadn’t been held under 20 pts since Dec. 10, a span of 11 games.