PHOENIX – Jalen Brunson hit the milestone on a night of 3-point perfection.

In a 139-122 upset victory that had the Knicks locker room in a celebratory mood, Brunson dropped 50 points on the Suns to give his franchise its first victory over Kevin Durant in over a decade.

Brunson was a flawless 9-for-9 on treys.

His final bucket, fittingly, was a 3-pointer with 1:46 remaining, placing Brunson in rare company.

He joined Kyrie Irving as the only two players in NBA history to score at least 50 points while not missing a 3-pointer. 

“That’s his franchise,” Durant said afterwards. “And he’s going to be a Hall of Fame player by end of his career the way he’s playing out there.”

The Knicks tend to win when Brunson connects from long range. 

Friday night certainly reinforced that.

The 50-piece bested Brunson’s previous top-scoring mark of 48 points, which he established last season.

He said it wasn’t on his mind as the game progressed, although his teammates were certainly aware and made sure to snag the game ball after the final buzzer.

“The good thing is we won and it just naturally happened through the flow of the game,” Julius Randle said. “I don’t think he was trying to go get 50 or whatever. He just was coming down making the right play, getting into his spots and hitting his shots.”

Maintaining his team-first persona, Brunson said of his special night, “It was cool. I’m just happy about the win. That’s all I really care about.”

But even Tom Thibodeau understood the significance.

He made it known with a joke at the expense of assistant coach Rick Brunson, a former role player on the Knicks who also happens to be Jalen’s father. 

“I told his dad, Jalen had his entire career in one night,” Thibodeau said.

Brunson, enjoying the best 3-point season of his career, bounced back emphatically from his 0-for-6 on 3s dud two nights earlier in Utah. 

He shot 17-for-23 overall and tied a career high with five steals. 

“It was quite a performance,” Thibodeau said. “The way he shot the ball was special. We probably didn’t take enough 3s, but 17 for 29 — he’s nine for nine. I told him after the Utah game that I love the way he played in Utah because he didn’t hesitate. He kept shooting. Shoots his shots. He works on his game everyday. And he works on all his shots that he takes in a game.

“His mental toughness is off the charts.”

The Knicks win snapped a 13-game losing streak to Durant, who went cold in the fourth quarter and finished with 29 points. 

Durant’s dominance over the Knicks spanned three different teams — OKC, Golden State and Brooklyn.

His last three victories with the Nets included a 53-point performance and two triple-doubles.

He relished the matchup against the outer-borough rival.

But it didn’t translate in his first matchup as a member of the Suns (13-12). 

The Knicks (14-10) improved to 4-9 against teams with winning records, which is relevant because Friday kicked off 10 straight games against opponents with winning records. 

Julius Randle and RJ Barrett combined for an efficient 43 points.

The Knicks shot 60 percent overall — including 59 percent on 3-pointers — mostly because Brunson’s shooting hand was aflame.  

For the Suns, the matchup represented just the second time the Big 3 played together — Durant, Booker, Beal — and their injury-free run Friday lasted less than five minutes. 

With 7:28 left in the first quarter, Beal turned his ankle badly after rising for a jumper and landing on Knicks guard Donte DiVincenzo.

It was a flagrant on DiVincenzo, who jumped into Beal’s landing space.

Beal limped off the court after taking the free throws and didn’t return. 

He has missed 19 games already this season with a back issue, raising red flags about Phoenix’s offseason trade for a player in the second year of a $251 million deal.

So the Suns were accustomed to playing without Beal, but they couldn’t stop Brunson, who scored 35 points in the second half.