WASHINGTON — Frank Ntilikina posted his career-high in points and became the youngest Knick to post a 20-point, 10-assist game.

It all went for naught, however, as Bradley Beal exploded for 40 points as the Wizards posted a 122-115 victory at Capital One Arena on Tuesday, with the Knicks blowing a 16-point halftime lead.

Ntilikina made 6 of 9 shots — 3 of 5 from the beyond the 3-point line. It was surprising he wasn’t in the game for much of the fourth quarter because Elfrid Payton (3 points, 1 of 5) had an off night.

After the Knicks fell behind 18-4 at the start, interim coach Mike Miller called timeout and yanked all five starters. Ntilikina led a 24-8 surge along with Bobby Portis, who finished with 20 points.

“Personally, I was just trying to change the game, make easy plays,’’ Ntilikina said. “Really, it was because of all five guys, I think, that had a good game. The ball was moving to the right shot at the right moment. Of course, it would have been better with the win, but I see improvement.”

Frank Ntilikina drives on Shabazz Napier during the Knicks' 122-115 over the Wizards.
Frank Ntilikina drives on Shabazz Napier during the Knicks’ 122-115 loss to the Wizards.Getty Images

Before the game, Miller had praised Ntilikina for his progress in driving the ball.

“I thought he played with a lot of command,’’ Miller said. “That’s the word that I’ve been using to describe him. He just played with a lot of command with his game. He did a good job with play calls, he was aggressive when he needed to be aggressive. He was in a good rhythm shooting the ball and got to the spots. He made shots. You know, I thought defensively, he was, you know, just like he always is. So I thought he was really, really solid throughout the game.”

The major issue with the 2019-20 Knicks is they don’t have an All-Star, like Beal, on the roster. That will be new team president Leon Rose’s challenge in the offseason — adding a star.

Before the game, Washington coach Scott Brooks predicted Beal will be an All-NBA selection.

“He’s one of the top 10 players in the league,’’ Brooks said.

And he proved all that versus the Knicks. He was 4 of 10 from 3 and sank 14 of 16 free throws.

“He was all over the floor,’’ Miller said. “He would come off of this first option and not have it and change sides of the floor and come off a different action. They were effective with that. And as we chased him around, we had a couple of sessions where we got crossed up in two guys with the same guy with the switches.’’

RJ Barrett has star potential but had a lousy outing Tuesday, and he got hurt late after getting hit in the mouth by Shabazz Napier. He finished with 16 points on 5 of 15 shooting. He was on the floor after getting hit and came up bloodied. Even though he stayed in the game, Barrett was checked for dental issues afterward.

The Knicks dropped to 20-45 and continue their three-game trip in Atlanta on Wednesday. There were a lot of Knicks fans in attendance, and they chanted “de-fense” with 2:30 left and the club down 10.