As feuds go the one between Isaiah Thomas and Danny Ainge didn’t have long legs. Then again neither does Isaiah.

The diminutive Cleveland Cavaliers point guard has been railing at the Celtics in general and Ainge in particular ever since he learned Ainge had shipped him out of town for Kyrie Irving. Thomas’ reaction, though a bit divaesque after a while, was understandable. So too was his ire at Ainge, with whom he thought he had a special relationship in a business where all relationships are, frankly, all business.

Still, Boston was the place Thomas became a star, the place where he ran the team, the place where he averaged a remarkable 28.9 points per game last season. It was the place Isaiah Thomas got to become Isaiah Thomas, at least the Isaiah Thomas he always envisioned. Danny Ainge was the one who gave him that chance.

As Thomas stood in a hallway between his old locker room at the Garden and his new one, chatting up a friend a half hour after concluding a pregame press conference, the bile seemed to have all drifted away when he saw Ainge walking down the hall toward him.

The smile that so often seems tattooed on Thomas’ face couldn’t be held back. How bitter can you be toward the guy who gave you your chance?

Thomas had just concluded talking about the love he felt for Boston, for the Celtics, for his old coach Brad Stevens and for Ainge, who he said texted him the night before his return to the city. But talk is one thing and bile quite another. You can say it’s gone but what happens when you’re face-to-face with the guy who sent you packing?

In Thomas’ case, you smile. Not smirk. Smile, exchange handshakes and half a bro’ hug and maybe, if Isaiah Thomas is wise, you move on. That’s what it sounded like he was doing last night before the Cavs squared off against the Celtics in as meaningful a regular-season game as you’re going to have this time of year.

This was Big Boy Basketball between the two best teams in the East, each trying to let the other know that when June comes around they’ll still be around, too. Isaiah was not a part of that though, the Cavs having decreed he is not yet ready for back-to-back NBA slugfests after recovering from the hip injury that ended his days in Boston in painful fashion seven months ago.

Thomas hadn’t played a minute this season until Tuesday night when he made his debut in maroon and gold in Cleveland. It didn’t take but one night to remind Cavs fans what Celtics fans came to know the past two seasons, which is that Isaiah Thomas is an explosive scorer who is fun to watch but not fun to guard.

In 19 minutes, he scored 17 points, admitting after it was over that he got a little winded at times and was sore when he woke up yesterday morning. Sore or not, he reminded those who’d forgotten that while Kyrie Irving may be a star, little Isaiah can shine pretty brightly himself, especially when he’s not bitching on Twitter about a cold-hearted business decision that had nothing to do with anyone’s love for anyone.

“He’s going to add quite a lot to that team,” Stevens said yesterday after noting he’d watched Thomas’ Cleveland debut. “You could tell that last night. He added a dimension, an element to their team.”

Isaiah Thomas added a dimension to himself last night in the amiable way he handled what had to be a disappointing return to Boston. Thomas lives to play basketball. It’s one reason he’s survived in a world that so often told him he was too small to survive. To not play, is to not be alive.

The resolve it took for him to do that while at the same time having to stand on a step ladder to look someone like LeBron James in the eye, is the same edgy stubbornness that made it so difficult to accept Ainge’s decision. To Ainge it was business. To Isaiah it was rejection and frankly he’d already had a bellyful of that.

But when he walked inside the Garden last night and saw so many familiar faces and remembered all the moments he’d had there on his way to becoming a star, he realized the truth is that the Ainge who shipped him out was the same one who gave him the chance others had denied him.

“They gave me the biggest opportunity I’d ever gotten,” said Thomas, who got a standing ovation when his image flashed on the video board between the first and second quarters. “I almost walked that way into their locker room (upon arriving yesterday). I love this city. I love this organization. They’ve given me the opportunity to be who I always wanted to be. I can’t thank them enough.”

Gone like that were the tweets and the harangues and the seemingly constant inability to let the disappointment of having been told to leave pass. Last night, Isaiah Thomas was back in Boston and glad to be there once more even if he didn’t quite belong any more.

“There’s no hard feelings to anybody in this city,” Thomas said. “No hard feelings to anybody in this organization. I’m glad I’m back. It’s genuine love. That’s for the rest of my life.”

OK. Fine. But what about toward the man who shipped you out? What about Ainge?

“He texted me last night,” Thomas said. “We’re good. The only hard feelings was he didn’t send me no Christmas card this year. He sent me the last two years. He could have found my address somehow.”

Thomas smiled at that. About 30 minutes later he smiled wider when he looked up and saw the man who traded him away walking toward him wearing the smile of a proud uncle. Maybe that’s when Isaiah Thomas first really remembered Danny Ainge was another guy, too.

He was the guy who gave him a chance “to be who I always wanted to be.”

Even in a Cleveland Cavaliers uniform, he’s still that guy.