Celtics can’t put away Cavaliers, who get 82 points from their backcourt in overtime win

Donovan Mitchell scored a season-high 41 points, including this dunk over Luke Kornet, on Friday night.Maddie Meyer/Getty

When this season began, there were questions about whether the Celtics were prepared for the expectations that followed them. Then they won their first three games and it seemed that there would be no speed bumps under interim coach Joe Mazzulla.

But the season is long, and it cannot really be distilled into segments as tiny as this one. The Celtics were walloped on the road against the Bulls on Monday, and against the Cavaliers on Friday they coughed up a 13-point lead, allowed Donovan Mitchell and Caris LeVert to pummel them, and ultimately were handed a 132-123 overtime loss at TD Garden.

It’s not exactly cause for alarm, but it’s not great, either.

“We have to learn how to win again,” Mazzulla said. “Each season, coming into it, you’re not guaranteed to win. So, it’s valuing the ball. And it’s knowing tendencies and boxing out and rebounding. Just the fundamentals. You just have to re-learn and constantly do them.”

For the Celtics, the fundamentals were hardly perfect. They committed 19 turnovers and surrendered a pair of critical offensive rebounds when LeVert came streaking in from the wings. Jayson Tatum air-balled a potential game-winning shot at the end of regulation.

Of course, if Tatum’s 20-foot buzzer-beater had gone in, the night’s narrative would have shifted. The Celtics would have shown their resiliency and gotten an MVP moment from their MVP candidate. But the shot missed, so the Celtics were left to explain why they are confident that this two-game skid will not swell into something more serious.

“We’ve got to keep piecing it together,” forward Al Horford said, “but I know that we can with the kind of group that we have. I know that we’ll do that.”

The Cavaliers were one of the NBA’s surprising teams for much of last season before sputtering down the stretch. But they made a seismic move this summer by trading for Mitchell and pairing him with another All-Star guard in Darius Garland.

Even though Garland has been sidelined since opening night due to a laceration under his eyelid, Cleveland continues to roll without him. When coach J.B. Bickerstaff was asked before the game about his “core four” that includes Mitchell, Garland, All-Star center Jarrett Allen and rising second-year big man Evan Mobley, he pushed back and said that this team’s depth goes beyond that group. Then LeVert, who erupted for 51 points against the Celtics two seasons ago, took the floor and poured in 41.

About 5 minutes after the final buzzer, the Cavaliers could be heard celebrating wildly behind the closed doors of the visitor’s locker room.

“I think we’re farther along than we expected [to be],” Mitchell said.

Jaylen Brown and Tatum had 32 points apiece for the Celtics, but those performances turned into footnotes. Tatum erupted for 24 during a dazzling first half in which the Celtics quickly flipped a 13-point deficit into a 13-point lead. But he later faced more constant double teams — reminiscent of last season’s playoffs — and had just eight points over the second half and overtime.

Boston lost despite shooting 51.2 percent from the field, and questions about the defense that was so dominant last season will now emerge. Through four games, Boston is surrendering an average of 115.3 points per contest.

“It’s tough when you have multiple players like that put that many points on your defense,” Horford said of LeVert and Mitchell. “But for us, it’s understanding that this is a new year and we have to be able to prove that again on that side.”

The Celtics had plenty of momentum heading into halftime but were stagnant at the start of the third quarter. A pair of misses in isolation situations were followed by a pair of turnovers, and the Cavaliers clawed back.

The Celtics still led, 112-108, with less than two minutes left in regulation before Mitchell converted a layup at the 1:51 mark. LeVert then grabbed an offensive rebound on a Mitchell miss and hit a 3-pointer with 1:10 left that gave Cleveland a 113-112 lead.

After Marcus Smart, who was just 3 for 15 from the field, was called for a travel, Mitchell missed a tough pull-up and it led to a fast-break that ended with a Brown layup that gave the Celtics a 114-113 lead with 28 seconds left. Allen was fouled inside and hit one of two free throws, but Tatum’s potential game-winner at the buzzer was an air-ball, forcing overtime.

“Got to where I wanted to,” Tatum said. “I guess I just kind of pushed it. But I was happy where I got to. I got to that spot. I feel like I practice that, work on that shot a lot. More often than not, it goes in.”

The Cavaliers pushed ahead early in the extra session and led, 121-116, when Mitchell hit a runner with 3:26 left. Brown answered with a 3-pointer and an emphatic one-handed slam as he was fouled. But he missed the free throw that would have given the Celtics the lead.

Boston committed turnovers on its next two possessions and LeVert, who scored Cleveland’s last 11 points, finished off the Celtics with a pair of free throws and a four-point play.