CLEVELAND — For three quarters Tuesday night, the Boston Celtics were in cruise control.

Then, in the blink of an eye, their 22-point, fourth-quarter lead over the Cleveland Cavaliers was gone. After a Jayson Tatum fadeaway missed long, and the Cavaliers successfully overturned a foul called on Darius Garland on the play, Cleveland emerged with a stunning 105-104 victory, snapping Boston’s league-leading 11-game winning streak.

“I think we are a much better team than we showed today,” Jaylen Brown said afterward. “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 gotta 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.”

For much of the game, it didn’t seem like any of those things were going to matter. Boston hit 50% of its triples through the first three quarters, It had a comfortable 16-point lead heading into the fourth — one that ballooned to 22 points when Tatum made a putback layup for a 93-71 lead with 9 minutes to go — and was playing a Cleveland team that entered the game missing Donovan Mitchell and Max Strus with knee issues and lost Evan Mobley to an ankle sprain late in the third.

Then the fourth quarter happened. Boston went 0-for-8 from deep, while Cavaliers forward Dean Wade went 5-for-5 from deep and 7-for-7 from the field — including a critical tip dunk with 19.1 seconds to go off a missed shot by Garland — as he outscored the Celtics 20-17 in the final frame.

“Rank’s pretty high,” Wade said with a smile when asked where that quarter stood among his personal accomplishments. “Pretty high. … It felt good. The rim looked really big.”

That offensive rebound was something Celtics coach Joe Mazzulla brought up multiple times in his postgame media session, along with several other mental mistakes and unforced errors Boston made down the stretch.

“We’ve given up offensive rebounds at the end of the shot clock when we were winning,” Mazzulla said. “I think that just, in situations like this, they just become a little bit more heightened and a little bit more attention to detail to them. But we’ve had take fouls in the backcourt before that didn’t hurt us because [it was a] different time of the game. And so 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.”

Then there was the final play of the game, after Wade’s tip dunk. Mazzulla initially didn’t call timeout, and Tatum brought the ball into the frontcourt, then had Derrick White set a pick for him to get the much smaller Garland switched onto him, before settling for a difficult stepback jumper on the right side of the lane that missed long.

It looked like Tatum (15-for-46 in clutch situations this season) would be bailed out when Garland was called for a foul. But Cavaliers coach J.B. Bickerstaff challenged the call and it was overturned, with crew chief Zach Zarba later telling a pool reporter that the contact made by Garland on Tatum’s leg was because Tatum kicked it out, and thus it was inadvertent contact.

“I knew the leg kick was kind of in play,” Garland said. “My shin still kind of hurts from it, so I’m glad it was overturned.”

Tatum had a different interpretation, though he also conceded he should have gotten into a play faster, instead of waiting for a final shot. Mazzulla said he tried to call timeout with just under 5 seconds remaining but that the referees never saw it.

“It was unfortunate,” Tatum, who went 1-for-9 in the quarter, said of the final possession. “I thought I got fouled … but they always say the game isn’t won or lost on the last play. There’s a lot of things that we didn’t do well in that fourth quarter that put us in that position.”

He was not wrong. Boston’s eight misses without a make from 3 in the fourth tied for the most without a make in a quarter by the Celtics this season, and it was only the fourth time this season Boston didn’t make a 3 in a quarter. The 17 points scored were the team’s fewest in a fourth quarter this season, and the Celtics were outscored by 17 — their worst point differential in a fourth quarter this season.

After seeing their league-leading win streak snapped, and heading into a potential NBA Finals preview against the Denver Nuggets on Thursday night, Brown said it was important to view this as a lesson in what not to do.

“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 no possessions, you can’t waste no time out there on the floor.

“So, today matters. We need to look at that.”