DENVER — Celtics coach Brad Stevens has long maintained that his team will go ­only as far as its defense takes it. And for much of this season, Boston has had one of the more dominant defensive units in the league.

But heading into Sunday’s 121-101 win against the Nuggets, it had slipped. Over four games, the Celtics had a defensive rating of 113.6, meaning that is how many points they allowed per 100 possessions. It was the worst mark in the NBA over that stretch.

“I just think we have to be much better into the ball,’’ Stevens said. “Listen, we’re small, and that’s something we have to make up for with presence and impacting the ball and not giving angles like we did the other night. I thought we just reached around and let guys drive right by us and get to the rim. And so if we’re going to be a good basketball team, we have to defend.

“And we have to defend with more presence than we did the other night. And we also didn’t play well against the Clippers defensively, or the Kings. Maybe the last time I thought we played really well defensively was at Cleveland. So we haven’t necessarily played that great on that end of the floor.’’

The Celtics seemed to snap out of their funk against the Nuggets, though, registering a defensive rating of 95.3. They are in third in the NBA with an overall rating of 99.8. The hope is that this recent stretch is more an aberration than the start of a concerning trend.

Recently, Stevens has often pointed out that the team must play defense with a better presence. On Sunday, he expanded on that notion, and what he is looking for from the defense.

“No. 1, you have an impact on the ball, but you’re solid,’’ Stevens said. “So you pressure as much as you can, but you’re still able to contain the dribble. You hold your ground, you show your hands, you do all those little things that end up winning.’’

Sullinger on rebound

Celtics forward Jared Sullinger had 16 points and 11 rebounds in Sunday’s win. Sullinger has now tallied 11 rebounds in four consecutive games. He had failed to reach double figures in rebounding in any of the five games before this streak.

“I’m just blessed to have the ball bounce the right way, I guess,’’ Sullinger said. “It’s best to have it come through my hands, I guess.’’

“We just need him to continue to do that,’’ Isaiah Thomas said, “continue to be a great rebounder and make shots.’’

Turner finds range

Evan Turner was just 8 for 61 on 3-pointers before the All-Star break. But he made 1 of 2 Sunday and is now 2 for 3 since returning from the break.

“I mean you’ve got to respect a 15 percent 3-point shooter, you know what I’m saying?’’ Turner said with a smile. “A guy like that is always lethal, so you can never really ease up. It’s 15 percent but it’s a big 15 percent.’’

Turner had 17 points and nine rebounds on Sunday.

­Avery Bradley bruised his right knee in the team’s loss to the Jazz on Friday night. He limped out of the locker room and did not sound optimistic about his chances of facing the Nuggets. But by Sunday afternoon he had been cleared to play, and that was a relief to the already shorthanded Celtics.

“It’s still a little tight,’’ Bradley said. “I’m just not thinking about it now. I went out and did my regular routine and it felt good. All credit to [trainer Ed Lacerte] and those guys, staying on me to take my medicine and keep the swelling down. And I’ve been getting a lot of treatment.’’

Bradley played 32 minutes and scored 20 points.

Marcus Smart, who sprained his right thumb on Friday, was cleared to play as well. He scored 10 points.

Lee headed to Dallas

Former Celtics forward David Lee cleared waivers Sunday and will officially sign with the Dallas Mavericks on Monday, Mavericks coach Rick Carlisle told reporters in Dallas. After beginning the season as the team’s starting power forward, Lee had slipped out of the rotation, playing in just one of the team’s 21 games before the All-Star break. Lee’s arrival in Dallas adds an interesting subplot to this season, as the Celtics will receive the Mavericks’ first-round pick in June’s draft as long as it does not fall in the top seven.

Absence noted

Forward Kelly Olynyk will be sidelined for several more weeks with a sprained right shoulder. Nuggets coach Mike Malone said his absence makes a big difference. “That second group is a challenge with or without Kelly Olynyk, but I think obviously they’re that much better when Kelly is healthy and playing,’’ Malone said. “So I hope his shoulder is fine and he gets back, but I’d be lying if I said I wasn’t happy he’s not playing today.’’

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