Jarrett Jack turned 33 at midnight Saturday. But Friday night, in the hours leading up to his birthday, Jack gave birth to a new role and gave new life to the young Knicks season.

In one swoop, Jack has gone from waiver-wire candidate when Joakim Noah’s suspension is done to starting point guard.

Jack who displaced Ramon Sessions and made his first Knicks start, was a steady hand in guiding the previously winless Knicks to a 107-86 victory over the Nets at the Garden. He secured eight points, five assists, seven rebounds and just one turnover.

Jack found out he would be starting after Thursday’s practice. With rookie Frank Ntilikina getting backup minutes, Sessions did not play and Ron Baker, struggling with a bum ankle since September, was deactivated.

Desperate Knicks coach Jeff Hornacek needed to organize the offense and put his trust in Jack.

“I’ve had some pretty good games in this building so hopefully it will translate into my homecourt now,’’ Jack said.

The move calls into question Sessions’ future after he started the first three games. When Noah returns after the 12th game, the Knicks will have to make a cut.

Jack, who has been a solid mentor to Ntilikina, said he did best getting Kristaps Porzingis “establshed’’ early.

“We were a lot more assertive just in our cuts,’’ Jack said.

“Jarrett did a great job whether he attacked or set up,’’ Porzingis said.

The offense had been disorganized and turnover-prone. The well-traveled Jack went against the Nets, his former team, with which he played from 2014-16.

The Knicks probably have the worst point-guard situation in the league.

“My job is to make sure the team is ready to play out of the gate,’’ Jack said before tip-off. “In Boston [Wednesday], our biggest hiccup was turning the ball over. I’ll try to spearhead that. Usually if the point guard does a good job of taking care of the ball, it’s usually contagious. If they don’t it goes the other way.”

Hornacek clearly wants a guy who will organize the offense better than Sessions, a driver.

“They’re both veteran guys who lead in different ways,’’ Hornacek said. “Ramon more a penetrating guy, Jarrett more a set-up guy.

Only one Net remains from the Jack days — Rondae Hollis-Jefferson. Jack knows Nets coach Kenny Atkinson, but never played for him. The Georgia Tech product lives in Atlanta, where Atkinson was a Hawks assistant coach and used to drop by the team’s facility to work out.

Willy Hernangomez finally got some meaningful minutes, playing in the second quarter. He played 13 minutes and scored four points, but was 0 for 4 from the free-throw line.

“It was great to be back on the court,’’ Hernangomez said.

Two late, legendary Knicks broadcasters will be honored by Fordham next week. Former Knicks analyst John Andariese will be feted with the “Johnny Bach Award” and Bob Wolff, who called both Knicks NBA championships, has won the “Vin Scully Lifetime Achievement Award. Knicks current broadcaster Mike Breen is a Fordham alumnus.