Isaiah Hartenstein reveals how agonizing the decision was to leave Knicks

LAS VEGAS — If the big offer came from a team other than the Thunder, Isaiah Hartenstein would have re-signed with the Knicks at a discount, the center told The Post. 

But the combination of a three-year, $87 million deal — with $58.5 million of it guaranteed in the first two years — and a chance for a championship was too difficult to turn down. 

“I was going to make sure I was set for the rest of my life,” Hartenstein said. “But then at the same time, if it wasn’t a team like OKC, I would’ve taken a pay cut because I loved it (in New York). But I now have an opportunity to make that money, make that pay raise, and still compete. I think that was the main factor.”

The Knicks, as Hartenstein confirmed in the interview Monday with The Post, made the biggest offer they could given their cap restrictions — four years, $72.5 million — which is about $11 million less annually than the Thunder contract.

Jalen Brunson participated in the pitch to retain Hartenstein. 

“They said whatever we can give you, we’re going to give you,” Hartenstein said. “I talked to Jalen a couple times, Jalen and the guys. They really wanted me back and I really appreciate that. But it was definitely a hard decision. I couldn’t say no to an opportunity like this.”

A couple weeks after Hartenstein’s departure in free agency, Brunson agreed to an extension at a hefty discount — a four-year, $156.5 million deal that could’ve been about $113 million more over five years if he waited until free agency next summer. 

Hartenstein, a journeyman through most of his six pro seasons with just $22.65 million in career earnings, explained why he wasn’t in the same position to make a sacrifice like Brunson. 

“He’s kind of in a different situation than I’m in. Already made $100 million (in his career). He’s the star player, knows he probably won’t ever get traded. So it’s a different situation,” Hartenstein said. “But that also shows what kind of a leader he is to make those sacrifices. I don’t think a lot of people are making those sacrifices. I think our situations are a little bit different but I have a lot of respect for him as a player and a human being for doing that.” 

Hartenstein became a pivotal part of the Knicks’ success while developing into one of their top analytical performers.

He started 49 games after Mitchell Robinson’s injury and boasted the team’s best net-rating last at +10, earning more playmaking freedom from Tom Thibodeau. 

Looking back on his two seasons in New York, Hartenstein said his favorite moment was grabbing the offensive rebound that led to Donte DiVincenzo’s dramatic go-ahead trey in Game 2 of the first round against the Sixers. 

The reaction from the Garden crowd was explosive.

“That was something special,” Hartenstein said. 

The Knicks still haven’t replaced Hartenstein, who was arguably their second-best player in the playoffs after Brunson.

Assuming the oft-injured Robinson starts again at center, the current backup is Jericho Sims. 

It’s the biggest position concern for the Knicks as they open their full-blown win-now window.

Hartenstein also enters the unknown as the center for a team that was established and stacked before his arrival.

His chemistry and connection to last season’s Thunder center, Chet Holmgren, is of paramount importance toward the team’s championship goals after they earned the No. 1 seed in the Western Conference last season.

In New York, Hartenstein was well-liked and social in the locker room, developing into a defensive leader and the team’s top paint presence. It was a situation almost too good to leave. 

Almost. 

“It was hard. For me if it wasn’t a situation like Oklahoma City with a chance to win, I don’t think I would’ve left. But that money is — you have to think about it, I just had a child so. …But it was really hard,” said Hartenstein, who became a first-time father last month.

“I love New York. I love the front office, I loved my team. So It was definitely hard. If it wasn’t a situation where I felt like I really had a chance to win, I probably wouldn’t have left.”