Zion Williamson is back in the Big Easy with a knee injury that could keep the Pelicans’ No. 1-overall draft pick out for a few weeks, so the Knicks’ RJ Barrett was presented a chance to steal the Garden stage from his former Duke roommate.

Barrett did just that, scoring 17 first-half points (though just two following the break) as the Knicks lost Friday for the third straight game in their preseason finale, falling 117-116 to the 5-0 Pelicans.

“He don’t look like a rookie,’’ coach David Fizdale said of the No. 3-overall draft pick, who also finished with three assists and six rebounds in 35 minutes.

A ragged Julius Randle came on for the Knicks in the fourth quarter, but shot just 7-for-18 to finish with 20 points against his former team and then didn’t rise up as the closer in the game’s dying moments.

Randle’s night was summed up in the final stages, when he intercepted a pass, then turned it over on a drive with 4 seconds left. After two missed free throws by New Orleans, Randle had one last chance to win it, lofting a 3-pointer that hit the back iron at the buzzer.

The Garden fans were in a frenzy the entire fourth quarter, inspiring Fizdale to walk into the interview room and blurt out: “Was that a playoff game? Our fans were awesome.’’

The Knicks ended the preseason with a 1-3 record and provided scant evidence they are going to outperform predictions of another season out of the playoffs. The Knicks open the regular season Wednesday in San Antonio and face a rough first three games with a Brooklyn-Boston back-to-back to follow the opener.

“The shorter preseason lends itself more to the teams [who are] established,’’ Fizdale said. “For teams like us, I wish we had eight games. You try to juggle it, see as much as you can in those four games to get a pulse of your team.”

Barrett was the star of the first half before going quiet. He drained 17 points, making 8 of 10 buckets and scoring on a transition 3-pointer off a feed from Smith. His power moves to the basket for a rookie shooting guard were impressive, especially getting to the basket on elite defender like Jrue Holiday.

“I feel I played well across the preseason,’’ Barrett said.

The outcome was all but sealed when Allonzo Trier, who did not play in the previous game, missed two consecutive 3-point tries on the same possession with under 30 seconds left and the Pelicans leading 116-114. Trier finished with 15 points.

The point-guard situation is messy, with neither of three battlers staging good enough preseasons to win the job outright.

That the Knicks may not get enough offense out of that position is growing clear. All three candidates — Elfrid Payton, Dennis Smith Jr. and Frank Ntilikina — are subpar perimeter shooters.

“I don’t want to have to think about it,’’ Fizdale said when asked if he has the winner. “They competed. They’re making it hard on me.’’

Smith started at point guard for the second straight game. He finished the night 2-for-12 for nine points. He racked up five assists and three turnovers in 31 minutes.

While he still couldn’t shoot straight, Smith ran the offense better than he did Wednesday against the Hawks, pushing the pace.

Payton had the better night with a good second half, but wound up with an uncharacteristic five turnovers, forcing too many passes. He finished with six points on 3-for-6 shooting with four assists in 17 minutes.

In the first half, Payton came on in relief for a modest eight-minute stint, though he made two strong defensive plays, blocking a shot and causing a turnover by poking the ball away from Holiday. He scored on a coast-to-coast layup, but also committed three turnovers before halftime.

Fizdale said beforehand he might use three point guards in a game.

The coach decided to start Wayne Ellington at shooting guard, move Barrett to the 3 and rest starting small forward Marcus Morris.

Randle said not to make anything of the 1-3 record, snapping, “It’s preseason.’’