Jaylen Brown believes the Boston Celtics' defeat to the Cleveland Cavaliers was a "mentality loss".

The NBA-leading Celtics threw away a 22-point lead in the fourth quarter of Tuesday's game, as they saw an 11-game winning streak come to an end with a 105-104 loss.

And Boston can only have themselves to blame, according to Brown, who finished with 21 points.

"I think we are a much better team than we showed today," Jaylen Brown said. "Today was just a mentality loss.

"We had the game and then we got comfortable, so it was more of a mindset thing than X's and O's.

"We've got to just be the more disciplined, the more militant team. We weren't that. Usually, we are that, and we felt that today and I think that's the reason why they were able to get back into the game.

"Our mindset was a little bit too lax, and we were too careless with the ball. We weren't intentional on offense.

"We kind of let guys get to tendencies that we were supposed to take away. We gave up offensive rebounds, stuff that all just comes with mindset."

Coach Joe Mazzulla echoed Brown's sentiment, citing defensive mistakes.

"We've given up offensive rebounds at the end of the shot clock when we were winning," he said.

"I think that, in situations like this, they just become a little bit more heightened and a little bit more attention to detail to them.

"They're the same situations that have been happening. They're just in more of a critical time. So it's a good heightened awareness to them."

Brown, meanwhile, asserted that the Celtics must learn from their mistakes.

"Today matters," Brown said. "Whether everybody wants to throw it away or not, we gotta look at the film and address some stuff, because that matters.

"Your habits are everything. Your mentality is everything. And every game, you can't waste possessions, you can't waste time out there on the floor.

"So, today matters. We need to look at that."

Dean Wade starred for the Cavs, going 5-for-5 from deep in their fourth-quarter revival, finishing with 23 points.

"Rank's pretty high. Pretty high," he said. "It felt good. The rim looked really big."