Dreams of a leisurely waltz to the NBA Finals?

More like Game 2 deja vu.

The Celtics had their streak of four consecutive blowout wins in the playoffs snapped Thursday with a 118-94 loss to the Cavaliers at TD Garden in Game 2 of the Eastern Conference semifinals.

The humbling defeat evened the series, which has begun to follow a familiar script for the top-seeded Celtics who routed the Heat in their first-round opener around a decisive Game 2 loss.

The Cavs weren’t historically productive from 3-point range like Miami was in its win, but they did make 46.4% of theirs to Boston’s 22.9%.

“In both of the games we lost here at home, we shot the ball incredibly bad,” Celtics forward Jaylen Brown said. “They shot the ball really well, and we didn’t play defense to our level tonight.”

Brown called the Celtics’ defensive performance “unacceptable.” Cleveland hadn’t scored more than 106 points in any of its first eight playoff games and managed just 95 in Game 1.

Spearheading Thursday’s effort was All-Star guard Donovan Mitchell, who scored 23 of his 29 points in the second half to go along with eight assists and seven rebounds. The Cavs also got a big night from Evan Mobley, who had 21 points, 10 rebounds, five assists and two blocks despite spending much of the second half in foul trouble. Six Cavaliers players scored in double figures, including Caris LeVert’s 21 points off the bench.

Jayson Tatum paced the Celtics with 25 points, seven boards and six assists.

Game 1 standouts Jaylen Brown (19 points) and Derrick White (10) struggled mightily from deep, going a combined 1-for-14 on 3s.

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The Cavs also out-rebounded the Celtics 44-31 and outscored them by 16 points in the paint despite missing injured starting center Jarrett Allen (bruised ribs). Boston also was down a key big man in Kristaps Porzingis (calf strain), and for the first time since his injury, it missed him.

“They did a good job, especially on pick-and-roll,” Celtics head coach Joe Mazulla said. “They tested our pick-and-roll defense. We have to do better at that. But a lot of that stuff in the paint came in transition because of our poor offensive spacing and our rim decisions at times.”

The Celtics, who won their first two games without Porzingis by 34 and 25 points, opened this one with a 14-5 run that prompted an early timeout by Cavs coach J.B. Bickerstaff. Four Boston players scored points during that opening flurry, with Al Horford and White both sinking 3s.

Cleveland quickly rallied, however, to tie the game at 19-19, then took its first lead of the game when was called for a foul while blocking a LeVert dunk.

The partisan Garden crowd didn’t like the call, but LeVert hit both free throws as part of a 9-0 Cavs run. Cleveland led 30-24 at the end of the first — the first time Boston had been outscored in any quarter since Game 4 against Miami.

The Celtics then responded with an immediate 9-0 run of their own, exploiting a small-ball Cavs lineup to score at the rim on three consecutive possessions.

After being outscored 22-6 in the paint in the opening 12 minutes, five of Boston’s first eight makes of the second quarter were layups or dunks — two by Jrue Holiday and three by Payton Pritchard.

The Celtics also got two second-quarter 3s from Horford and one from Tatum, then went cold, making just one field goal over the final 4:53 of the first half. Boston entered halftime tied 54-54 after a sloppy Brown turnover and foul gifted Cleveland foul shots in the final seconds.

The Cavaliers then controlled the pace of play during a lopsided third quarter, led by their talented backcourt duo of Mitchell and Darius Garland.

Mitchell shook off his sleepy, six-point opening half to score 16 in the third, including a buzzer-beating 3-pointer. Garland added nine points in the frame as Cleveland’s lead swelled to double digits.

“He made some tough shots tonight,” Brown said. “Some tough contested threes. We’ve got to be up. He’s a basketball player, and we’ve got to have a little more alertness to him. Tonight, he got the best of us.”

Mobley picked up his fourth foul with five minutes remaining in the third, forcing him to the bench. But the Celtics couldn’t capitalize against his replacement, past-his-prime veteran Tristan Thompson. Cleveland took a 90-78 lead into the fourth quarter and never looked back.

Mazzulla emptied his bench with five minutes remaining, giving rookie guard Jordan Walsh the first postseason action of his young career.

The Celtics rebounded from their ugly Game 2 loss to the Heat by reeling off three straight routs to win that series in five. Mazzulla will be hoping Thursday’s clunker spurs a similar turnaround.

“You treat it the same way you would a win,” the coach said. “You come in tomorrow, you watch film, and you get better for Game 3.”