BOSTON -- It is no coincidence that the Cleveland Cavaliers turned in their two best defensive efforts of the season the past two games, the first two for Iman Shumpert after his recovery from wrist surgery.

However, Shumpert, the defense-first guard who helped Cleveland to an 89-77 victory over the Boston Celtics on Tuesday night, left the game with a groin injury.

"Honestly, (I am) a little bit concerned," Cavaliers coach David Blatt said after Shumpert left the game after playing just 13:32, a performance that included two big 3-pointers early in the fourth quarter. "I have no idea what the extent, is but given what our recent history is, I'm concerned."

The Cavs (16-7) are close to getting star point guard Kyrie Irving back for his season debut after his recovery from a knee injury. There is no way of knowing how long Shumpert, who missed the first 21 games of the season, will be out.

Cleveland held Orlando to 38.9 percent shooting and 76 points on the road Friday night, then limited the Celtics to 32.2 percent from the floor -- and to 31 points in the second half. Blatt credited Shumpert's return and the play of center Timofey Mozgov (nine points, 10 rebounds Tuesday) for the defense.

Oh, and forward LeBron James.

The coach went out of his way to credit James' oft-overlooked defense as a key.

"It seems like there's nothing we don't ask of him that he doesn't answer for us," said Blatt. "That's why he's the greatest player in the game."

James shot 10-for-20 from the floor and scored 24 points while grabbing seven rebounds and turning the ball over six times in 35:42.

Cleveland forward Kevin Love, playing his first game at TD Garden since his postseason ended when Boston forward Kelly Olynyk tried to separate his shoulder from its socket, had 20 points, eight rebounds and five assists.

Talking about the team defense, James said, "That's one of our staples we stress every single day -- defending at a high level and trying to move the ball offensively. In the first half, we allowed them to get to some of their spots. Wasn't as aggressive, but we still played very well.

"They had 46 points at halftime. But in the second half, we just locked down and then we started moving the ball. We just kind of kept them off base."

James capped a 12-0 third-quarter run with a reverse slam dunk, his fifth and sixth points during the spurt. When Boston (14-11) closed within seven, Love hit six points and James two in an 8-0 run that sent folks heading for the exits.

Guard Avery Bradley led the Celtics with 17 points, while forward Jae Crowder, who played strong defense on James much of the night, added 14. Guard Isaiah Thomas shot 3-for-15 from the floor en route to 12 points.

The Celtics, who rebounded from their double-overtime loss to the Golden State Warriors on Friday night with a win at Charlotte on Saturday, have to play at Detroit on Wednesday night.

"We're going to have to play a lot better than we did tonight to have a chance to win," Boston coach Brad Stevens said.

After the physical confrontations that knocked Love and Crowder out of last year's playoffs, there was the thought there might be a continuation in this first meeting of the season. Things got a bit sticky late in the second period, when Cleveland guard J.R. Smith, who knocked Crowder out of the playoffs, took Thomas down the a hard foul and Crowder was involved in some talking.

On Cleveland's next possession, a Boston foul led to Crowder clapping near James. Nothing else happened.

Smith finished with nine points and six rebounds, and his defense helped hold the Celtics to a season-low point total.

NOTES: After the game, Cavaliers F LeBron James met with 16-year-old Aaron Miller, a local boy who was born with severe brain damage that doctors said would paralyze him physically and mentally -- and gave him his shoes. Miller was wearing a pair of James' specialized shoes made for disabled children. "This game is so much more than basketball," James said. "When I saw that and when I saw his story, it was just like, I don't know, I felt like I was a part of him, so I just showed him my respect and gave him my shoes and it was well received by him. It's not for (the media), it's not for the fans, it was for him." ... The 77 points scored by the Celtics matched the second-lowest point total in the three-year Brad Stevens coaching run. ... Boston rookie G R.J. Hunter (hip) returned after missing four games and logged 2:40, failing to score. Boston was still without G Marcus Smart (leg), who missed his 12th consecutive game.