CLEVELAND -- Before Sunday night's game against the Boston Celtics, Cleveland Cavaliers coach Kenny Atkinson said he wanted to see what his team would look like after back-to-back losses to the Atlanta Hawks -- the first adversity it has faced this season.

Then, when the Cavaliers found themselves down by 14 in the third quarter, it felt like they could potentially get run out of their own building by the defending champions, who were without Jaylen Brown (illness) and Derrick White (foot).

"That was kind of my question mark a little bit with this team after those two losses to Atlanta," Atkinson would say later, "and it looked like we were down and out that third quarter.

"They were rolling, the crowd was kind of down, we were all kind of down."

All of the Cavaliers, that is, except Donovan Mitchell. Instead of watching the game slip away from him, and his team losing for a third straight time, Mitchell put the Cavaliers on his back, scoring 30 points in the second half -- including 20 points in the fourth while going a perfect 6-for-6 from the field -- to outduel Jayson Tatum down the stretch and lift Cleveland to a 115-111 victory.

"In the third," Mitchell said when asked when he realized he was going to have to take over the game. "I kind of felt it then, especially -- and I'm going to be selfish when I say this -- when [Tatum] hit a shot over me.

"I was like, 'He's starting to get it going, they're starting to get confidence, they're starting to build, we're turning it over.' ... In the third, I was just waiting, just trying to figure out where to go.

"And then, when I came back in the fourth, kind of be like, 'All right, give me the ball. It's time to go.' And I was just telling somebody, 'Shots may not fall. I may go 0-for-6.' But you know what? You have to find a way to be like, 'I'm going to be aggressive right here. Get to my spots and if we go out, we'll go like this.' And that's what tonight was."

Mitchell said the third quarter reminded him of Game 3 of Cleveland's Eastern Conference semifinal series against Boston, when the Celtics opened the third quarter with 14 unanswered points -- putting the Celtics on a path to not only win that game but the series.

But unlike that game, when the Cavaliers wilted, they fought back Sunday night, largely behind a sublime performance from their headlining star, who knocked down three triples in a 93-second span late in the fourth to erase a Boston lead and tie the game, and then put Cleveland ahead with a runner in the lane with 1:07 remaining -- a bucket that gave the Cavaliers a lead they would never relinquish.

With the win, the Cavaliers retained their hold on the NBA's best record at 18-3, ahead of the 16-4 Celtics.

"That's Donovan's persona," Atkinson said of how Mitchell willed Cleveland back into the game. "It's amazing, I've never seen a guy [like him].

"He never gets down. You'd think guys would kick the chair or get frustrated. He has a great demeanor about him and never gets too down or too high. He's much better than the coaches in terms of that.

"He's just like, 'Everybody calm down, it's going to be all right.' And I think that really helps you bounce back from a poor first half like that."

The Cavaliers also repeatedly allowed Darius Garland, their 6-foot-1 point guard, to get matched up against the 6-foot-8 Tatum down the stretch, turning Boston into an isolation team and getting the Celtics out of their usual ball-movement-heavy offense.

It worked, too, as Tatum -- who finished with 33 points, 8 rebounds, 4 assists, a steal and a block in just under 38 minutes -- went 2-for-7 from the field in the fourth as Boston saw its lead evaporate.

"I mean I was getting in my spots all night, attacking the mismatch and things like that," Tatum said. "Probably the last four minutes they kind of started double-teaming. ... So find somebody that was open and just try and make the right play."

Atkinson said repeatedly during his postgame news conference that he has challenged Garland to take on defensive matchups, saying he doesn't want to hide him come playoff time. Garland said he's up for it.

"He never gets down. You'd think guys would kick the chair or get frustrated. He has a great demeanor about him and never gets too down or too high. He's much better than the coaches in terms of that."

Cavaliers coach Kenny Atkinson on Donovan Mitchell

"I'm going to take that challenge whenever it is," Garland said. "I'm no punk. So if y'all want to switch and try to X me out and try to just hunt me out, that's cool. I ain't no punk, though. I'm going to take a challenge."

After starting the season 15-0, the challenge for Cleveland entering this game was to staunch the bleeding after dropping three of its past five games.

And while there's still a long way before a potential rematch with Boston in the playoffs, this was a game the Cavaliers could point to as a sign of positive growth.

"I think that just speaks to the growth of our group," Mitchell said of the comeback. "I think you go back to when I first got here, obviously we're younger, we're not as familiar with each other, [and we'd] kind of fold in those situations.

"You're just seeing the growth, and that's the biggest thing I feel like is for us just continuing to build ... if we continue to grow and continue to learn from these different things, that's really what it's about. That's what tonight was. We could have easily been like, 'All right, turning the ball over, different things, not getting stops, offense kind of bogged down.' But who were we when we hit adversity? And that's what I've been saying. It's great to learn through these wins, but when we face adversity, who are we going to be? And that's what you're continuously seeing from this group. We've been trying games and different things, and so I'm proud of the way we fought."