LeBron James limped off with leg cramps two times in the second half.

He wasn’t worried about the outcome. By now, he knows the depth of the Miami Heat roster. And on ring night, there was no way the reigning NBA champions were going to have their party spoiled.

Dwyane Wade scored 29 points, James finished with 26 points and 10 rebounds despite spending parts of the third and fourth quarters hydrating in the locker room, and the Heat beat the Boston Celtics 120-107 Tuesday night in the season opener for both teams.

“A night that we won’t forget,” James said.

That’s true, for a lot of reasons.

There were actual fireworks before the game to close the ceremony where the Heat got their championship rings and raised their title banner. There also were plenty of figurative fireworks late, first with Boston almost digging out of a 19-point hole and, after the outcome was decided, Rajon Rondo flagrantly fouling Wade by wrapping his arms around his neck on a drive.

In the end, though, the first Celtics-Heat matchup of this season was like the final one of last season — with Miami winning.

“It was good to cap this night off with a win,” Heat coach Erik Spoelstra said.

Chris Bosh was dominant late, finishing with 19 points and 10 rebounds. Allen scored 19 points — needing only seven field goal attempts — in his first game with the Heat since leaving Boston over the summer.

Allen got chants from the Heat crowd, which is nothing new. Except this time, they were positive.

“Never thought I’d hear that here,” Allen said.

Paul Pierce scored 23 points, Rondo finished with 20 points and 13 assists, and Leandro Barbosa scored 16 for Boston. The Celtics, who lost to the Heat in last season’s Eastern Conference finals, were not on the court for the ring ceremony.

They almost wrecked the festive mood with a late comeback.

An 11-2 run late in the fourth quarter got Boston within 111-107 on Courtney Lee’s layup with 2:09 left. That was the last Celtics’ hurrah — Bosh scored the game’s next seven points, sealing it for Miami.

“I thought they were the aggressor the whole game,” Celtics coach Doc Rivers said. “They got on the floor where they wanted to get on the floor. They took us out of stuff that they wanted to.”

Rashard Lewis scored 10 points for Miami, which held on even while James, last season’s MVP of both the regular season and NBA Finals, dealt with cramps, first in his right leg and then his left.

The Heat got their championship rings from owner Micky Arison before the game, then watched the banner get hoisted to the rafters. More emotion came late, when Wade drove past Rondo — and the Celtics guard grabbed Wade around the neck. Wade appeared as though he was ready to throw the ball at Rondo in retaliation, and stopped himself.

While Rondo raised eyebrows by putting hands on Wade, Kevin Garnett made news by not offering his hand to Allen.

As Allen entered the game for the first time, he trotted toward the Boston bench, exchanging a handshake, embrace and a few words with Rivers, who hasn’t hidden his displeasure about his former shooting guard’s decision to sign with Miami and didn’t sound certain before the game how he would react when he saw Allen in Miami colors. Allen then briskly shook hands with a few assistant coaches.

But when Allen tried to engage Garnett, the mutual pleasantries ended. Allen tapped Garnett on the shoulder as he sat on the Boston bench; Garnett didn’t even flinch, staring straight ahead, refusing to acknowledge the gesture in any way.

“I was just trying to focus as much as I could. I am such an intense person,” Garnett said. “It was a blank. Obviously he’s on the other side. It’s time to play the game, man.”

NOTES: Wade passed the 15,000-point mark for his career early in the second quarter, becoming the 123rd player in NBA history to reach that mark, according to STATS LLC … Rondo had at least 10 assists for the 25th straight regular-season game.