It was a rough night for the Knicks point guards Dennis Smith Jr. and Frank Ntilikina trying to shut down Atlanta’s Trae Young. Both got into foul trouble and were ineffective on offense in the Knicks’ 100-96 preseason loss Wednesday to the Hawks at the Garden.

The derby to be starting point guard could be won by the guy who got the night off — Elfrid Payton. Knicks coach David Fizdale huddled with Payton before the game and told him he needed to see Smith and Ntilikina.

Smith, making his preseason debut after missing the first two games with a back strain, looked out of sync after picking up two fouls in the opening 2:23 and headed to the bench.

Smith finished with four points on 1-of-5 shooting and was credited with three turnovers and three assists.

“Absolutely,’’ Fizdale said when asked if Smith was rusty. “Especially offensively. No rhythm at all. He has to play through that stuff and start shaking it off.”

Ntilikina did better. He turned in a solid job on defense late, but scoring remains a painful issue. The Frenchman came in for Smith after two minutes and picked up a quick pair of fouls while trying to guard Young, but was kept in the game. Ntilikina spurred the Knicks’ late defensive charge with a key block on Young and an interception of an inbounds pass with 25 seconds left. But he registered just two points on 1-of-4 shooting to go along with two blocks and a steal.

Smith and Ntilikina combined for six points.

“We still got a long ways to go from a trust standpoint,’’ Fizdale said.

Ntilikina and Smith said they were pleased to hold Atlanta to just 100 — each citing defense being the club’s new identity.

“We didn’t play the way we wanted to play on offense,’’ Ntilikina said. “But it’s only the third preseason game. We know defensively we can be a good team. The offense will come.’’

Fizdale would only praise Smith and Ntilikina for fighting against Young, who went off for 23 points, including a 35-footer at the third-quarter buzzer, and nine assists.

“They battled,’’ Fizdale said. “Trae is a heckuva player. Dennis and Frank really competed against him.’’

In the first half, Smith bricked a long jumper, lost the ball at the key for a turnover that resulted in fast-break points for Atlanta and then was called for traveling. He was scoreless in 10 first-half minutes.

“It was tough to get a rhythm, trying to get my wind back,’’ Smith said. “I have to get my wind all the way up and get my rhythm back.”

Despite a reputedly improved jumper, Smith didn’t look sharp in the second half either. He was doubled on a drive and showed little poise under pressure, getting caught in the air and throwing it into Young’s arms.

After missing his first four shots, Smith finally hit his first bucket with 4:55 left — a 20-footer to tie the score at 91.

“I was like, ‘Damn, about time,’’’ Smith said.

But then Smith’s pass, trying to feed the low post, was intercepted on the next possession by DeAndre’ Bembry.

Fizdale said before the game Ntilikina would play “significant minutes’’ — the first hint Fizdale was willing to give Payton the night off. One theory is Fizdale knows what he has in Payton, the pure playmaker and good defender who started the first two preseason games.

The Knicks have one more preseason game Friday versus Zion Williamson’s Pelicans, and they need to find out what Smith and Ntilikina can deliver in their third seasons.

Rookie RJ Barrett manned the point at times, but his shooting was erratic. Barrett couldn’t hit an outside shot, but got to the basket easily. Nevertheless, he missed too many easy shots around the rim and finished 4-of-14 for 12 points.

Forward Julius Randle finished with 20 points, but missed a game-tying free throw with 19.2 seconds left.

Ntilikina’s contract option for his fourth year has an Oct. 31 deadline. Smith’s option faces a similar deadline, but it would seem difficult for Knicks brass to pass on executing it, considering he was the key piece of the Kristaps Porzingis trade.

Was Ntilkina also being showcased? There have been suggestions in Detroit the Pistons may have some interest. Pistons executive Malik Rose, a former Knick, was at the Garden for the game. The Post reported last season the Pistons asked about Damyean Dotson, who did not play Wednesday.

Earlier in the day, TNT’s Stan Van Gundy said he figured Smith would wind up as the starter. It doesn’t look that way now.

“My guess is they give Dennis Smith first shot at it,’’ Van Gundy said. “They traded for him he’s still on a rookie contract. He’s got explosiveness. If he can improve his decision-making and shooting …’’

It marked the first time since they became teammates that Ntilikina and Smith were both active for the same game, which says a lot about their injury histories.