BOSTON — Kristaps Porzingis didn’t want to make predictions about how his body would respond heading into the NBA Finals after he spent more than a month on the sideline with a calf injury.

Just fine, it turned out.

Jaylen Brown scored 22 points, Porzingis made an immediate impact off the bench and added 20 and the Boston Celtics powered past the Dallas Mavericks 107-89 on Thursday night in Game 1.

Derrick White finished with 15 points for Boston, which led by 29 points in the first half and connected on 16 3-pointers in a powerful start to its quest for an 18th NBA title.

Porzingis, a 7-footer who had been sidelined since April 29, added six rebounds and three blocks in 21 minutes.

“Tonight was affirmation to myself that I’m pretty good,” Porzingis said. “I’m not perfect but I can play like this and I can add to this team.”

The last Celtics player to enter the court for pregame warmups, he said he received a jolt of energy from a home crowd, which erupted when he emerged from the tunnel.

“The adrenaline was pumping through my veins,” Porzingis said.

Celtics coach Joe Mazzulla wasn’t concerned about the layoff affecting Porzingis’ aggressiveness.

“That’s the KP that helped us get to where we are today,” Mazzulla said. “It doesn’t matter how long the guy is off, he’s going to make plays.”

All-Star Jayson Tatum finished with 16 points and 11 rebounds. Six players scored in double figures for the Celtics, who host Game 2 on Sunday.

“Getting back to this point and being here is really a big deal,” Tatum said. “But two years ago we won the first game and we know the outcome of that series. We still have a lot of work to do.”

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Dallas Struggles to Find Offensive Consistency

Dallas cut the deficit to eight points in the third quarter, but Boston answered with a 14-0 run to quickly pull away again.

“That’s when the game started,” Brown said.

Luka Doncic led Dallas with 30 points. P.J. Washington added 14 points and eight rebounds. But Dallas couldn’t find offensive consistency beyond that, totaling just nine assists on its 35 field goals for the game. The Mavericks didn’t score 25 points in any quarter.

Doncic said the lopsided loss wouldn’t diminish the spirit of a team that lost the opening game in three of four series this postseason.

“Either you lose or you win,” Doncic said. “First to four, we’ve got to focus on the next game.”

Former Celtic Kyrie Irving struggled throughout, finishing with 12 points. He received a loud and extended chorus of boos Thursday when he was introduced before the game. It continued throughout the game whenever he touched the ball.

The treatment came after Irving sparred with Boston fans and was fined for using an obscene gesture during a 2022 playoff visit to TD Garden.

“I thought it was going to be a little louder in here. I’m expecting the same thing (in Game 2). The crowd’s trying to get me out of my element,” Irving said. “It’s not the first time I’ve lost in Boston. I don’t want to make it a habit.”

Celtics Show Little Rust From Layoff

The Celtics, seeking their first championship since 2008, showed little rust from their 10-day layoff after sweeping the Indiana Pacers in the Eastern Conference finals.

They flowed with energy throughout, sharing the ball in the halfcourt and getting the ball to shooters for open 3s. They also attacked the interior of the Dallas defense and got to the rim for several dunks.

Meanwhile, apart from Doncic, who shot 12 of 26 from the field, Dallas struggled early to get into its sets and couldn’t find a consistent groove offensively.

The Mavericks led by one midway through the first quarter. The Celtics responded by outscoring them 44-16 to make it 58-29 in the second.

Things changed over the next 12 minutes of game action when Dallas used a 35-14 run, including 15 points by Doncic, to cut Boston’s lead to 72-64. But the Celtics were back up 86-66 entering the fourth.

Dallas had just five assists through the first three quarters, the fewest any NBA team has had through 36 minutes in any game in the last three seasons.

“We’ve got to move the ball,” Dallas coach Jason Kidd said. “The ball got stuck too much.”

Porzingis ended his 10-game hiatus when he came off the bench with 7:17 left in the first quarter in place of starter Al Horford. With the exception of a white compression sleeve on his right leg, it was hard to tell Porzingis was coming off an injury.

He got into the mix quickly, knocking down a pair of free throws after being fouled by Doncic. A possession later, the Latvian connected in his first field goal when he dropped on a short jumper over Doncic.

He wasn’t done.

Minutes later he got loose in the paint for a two-handed dunk over Derrick Lively. On Dallas’ next possession, Porzingis was there to swat away Jaden Hardy’s layup attempt. The Celtics pushed the ball up the court and got the ball back to their big man, who calmly buried a 16-footer.

It was part of a 17-5 surge by Boston over the final 5:24 of the quarter that saw Porzingis go 4 for 5 from the field, score 11 points, block two shots and grab three rebounds. Boston carried a 37-20 lead into the second quarter.

Porzingis finished the half with 18 points on 7-of-9 shooting.