If you were paying attention, then your attachment to Jalen Brunson didn’t begin on Oct. 19, the Knicks’ opening night at Memphis, when his 15 points, nine assists, zero turnovers and the holy-cow-did-you-see-that charge he took against Ja Morant all helped force overtime against the Grizzlies.

It didn’t begin in those opening weeks of the season, when — maybe for the first time this season, maybe for the first time in several seasons — you could tune into a Knicks game, see Brunson running the show on both ends of the floor, and instantly say: This just looks … different. Better.

Professional.

No, if you were really paying attention, then you latched onto the Mavericks right around this time last year. By then, it was understood that the Knicks were going to make a big play for Brunson in the offseason. Maybe you were familiar with Brunson’s work at Villanova. Maybe you’d seen him steadily improve in all four seasons in Dallas. Maybe you thought: Nice player. Good player. He’d help.

But then you watched Dallas start the playoffs against Utah and its star, Donovan Mitchell. You watched the Mavs take out the Jazz in six despite missing Luka Doncic for the first half of that series. In the four games the Mavs won, these were Brunson’s numbers: 30.0 points, 54 percent shooting.

In what was probably the most important game of the Mavs’ entire run to the West finals, missing Doncic and having already lost Game 1 at home, this is what Brunson did against the Jazz in Game 2: 41 points, eight rebounds, five assists, two steals, 60 percent overall, 6-for-10 from 3-point range.

Maybe you grew attached then. Tom Thibodeau was already smitten.

“If you paid attention whenever they had people out in Dallas, he always played well,” the Knicks coach said Tuesday, as his team gathered for the first time to prepare for Game 1 of their playoff series with Cleveland, starting Saturday at Rocket Mortgage Fieldhouse.

“When he filled in, started. And just having been around him what he did in high school, state tournaments and at Villanova. Big games. He’s always played his best in big games. We all knew that. That’s just who he is. He’s gotten better every year. And his game translates. He can think on his feet. He can read defenses well. He knows where the holes are. He’s got a very fundamental game.”

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Yes. If you paid attention, you already knew the Knicks had probably made their smartest acquisition in decades when they signed Brunson to a four-year, $104 million deal in July. And if you’ve paid attention at all this year, you know that was maybe the best bargain in basketball since Jimmy Chitwood agreed to play as long as Norman Dale would stay.

“I think most importantly is it wasn’t just me,” Brunson said Tuesday. “It was how this team embraced me with open arms. How they’ve let me be myself, play the way I play. The relationships we’ve made this year, it’s been great. It wasn’t just me — it was a credit to everyone — building, sacrificing and just wanting to win. We were able to get to a decent place in seeding. We have a long way to go for us to get to where we want to go.”

That starts in the playoffs, and that’s where Brunson’s remarkable story can take on an even greater sense of fairy tale. The Knicks have won one playoff series — one — since 2000. They haven’t won a series in which they didn’t have home-court advantage since they beat the Heat in the 2000 East semifinals. It is a franchise crying out for playoff prosperity.

And Brunson knows it.

“We know what [the Cavaliers] are capable of,” he said. “We know they play really well at home, and they obviously have home-court advantage first round. We’ve just got to be at our best. They’re a great team. We have to be at our best.”

And there is no reason not to expect that from Brunson. It’s what he does. Part of the legend of Dave DeBusschere (and it is inarguable that Brunson has been the single-most-important Knicks acquisition since No. 22) is that, after he transformed the 1968-69 Knicks and led them to the doorstep of contention, he averaged 21.3 points and 17.5 rebounds in his very first playoff series, against the Baltimore Bullets in March and April of 1969.

DeBusschere’s first playoff game as a Knick? Twenty-four points and 21 rebounds in a franchise-altering, 113-101 Game 1 win at Baltimore that ignited a stunning sweep.

“All we’ve done, all I’ve done, we knew we had to do it in the playoffs for people to really believe it,” DeBusschere said that night. It was his mission to deliver. He delivered. Brunson knows that conviction. He has already been there.