For Ray Allen, the renewal of the Boston-Miami rivalry must have been an out-of-body experience.

At certain surreal moments Tuesday night, he must have observed himself wearing a burning red basketball on his jersey instead of a green shamrock and wondered, “Where am I?”

He was the object of Kevin Garnett’s snarls rather than beneficiary.

He fed an assist to Chris Bosh, patted the shoulder of Dwyane Wade, unleashed a fast break for LeBron James. He was aiding his former sworn enemies.

He was fouled by Paul Pierce, the mate who used to have his back in bruising battles against the Heat.

He watched the NBA championship banner-raising ceremony of the team that crushed his own championship aspirations.

What was he supposed to do in such a situation? Celebrate or congratulate?

Miami’s 120-107 victory over the Celtics in the season opener for both teams turned Allen’s emotions inside out. It was his first game in a Heat uniform, against the team to which he devoted five memorable years, on the very court where he played his final game as a Celtic, in a bitter Game 7 loss in the Eastern Conference finals.

Allen insisted there was “nothing personal” about the latest chapter in what has become the NBA’s most interesting recurring grudge match. Once the ball goes up, the goal is clinically straightforward: Beat the opponent.

But of course Allen’s first encounter with the guys he shed blood, sweat and tears with must have been gut-twisting. He hadn’t communicated with them since his unhappy departure from Boston as a free agent during the offseason.

Just before he entered the game with 2:45 remaining in the first quarter, Allen dashed over to the Boston bench and went down the line, slapping palms. He called it his “peace offering.”

STRAINED FEELINGS REMAIN

“They can be angry at me but they are my friends and I’ll always appreciate what they did for me,” Allen said, emphasizing that he harbors no animosity for players with whom he won the 2008 NBA title. Garnett didn’t acknowledge Allen when he made the gesture. “But that’s KG. He’s an intense competitor and when he’s on the bench he’s in a different zone.”

Allen had a strained relationship with Rajon Rondo the last two seasons, “but he came over and said, ‘What’s up?’ There’s no hostility,” Allen said.

Allen, 37, the NBA’s all-time three-point leader, was a key acquisition for the Heat in its drive for a Heat-peat. Why not remove a thorn from your side and turn it into a weapon?

And Allen was effective, scoring 19 points in 31 minutes, getting to the free throw line eight times and sinking two three-pointers.

“It was like watching TV seeing Paul run up and down,” he said. “I had to ask myself who I was guarding, which team I was guarding at times. My brain has to be switched over.”

On Allen’s first attempt, he sank his signature three-pointer from the corner over Jason Terry, the guy the Celtics hired to replace him. He was fouled sort of half-heartedly by Pierce, No. 34 swiping at No. 34. Allen swished both free throws. He hit a difficult three over Courtney Lee, a leaning bank shot over Terry and a free throw following a technical on Rondo.

“I love playing with Ray,” Wade said. “The space – people will be paying attention to him.”