SAN ANTONIO — The rave reviews Knicks rookie RJ Barrett received for his preseason mean “nothing.” That’s according to Barrett on the eve of his real NBA debut, when the Knicks open their season in San Antonio on Wednesday night.

“I mean preseason, it counts for nothing,’’ Barrett said Tuesday after their final practice in Tarrytown. “So tomorrow is where the real evaluation begins.

“I’ve been here for a while, getting used to it but now it’s like real. It’s real. As soon as I run out on the court, I’m going to feel a different type of vibe and different tension. I’m going to go out on the court and have fun with it.’’

The No. 3 pick of the draft erased the bad vibes coming out of his disjointed summer league in Las Vegas, sparkling during the four-game preseason. Knicks coach David Fizdale admitted he never wanted to take the 6-foot-7 shooting guard off the court as he was arguably his team’s most valuable player.

“If anybody is up for it, it’s that kid,’’ Fizdale said of Barrett’s debut. “I’m not expecting him to work miracles. I just want him to be himself like he’s been doing.’’

Fizdale has called Barrett “fearless’’ on multiple occasions and he has showed a terrific knack of using his strong, 19-year-old frame to muscle to the hoop for buckets in preseason games against Washington (twice), Atlanta and New Orleans.

But now it’s the mighty Spurs, coached by one of the league’s all-time defensive wizards in Gregg Popovich.

“It’s going really well so far,’’ Barrett said. “I definitely think I’ve prepared myself well. I got to keep going and kick it up to another notch now.”

It doesn’t get that much easier early on as the Knicks then play in Brooklyn on Friday before the home opener against Boston.

“I feel the first couple of games are definitely going to be more emotional,’’ Barrett said. “Everything picks up a notch. Preseason to the regular season to the playoffs is different, too. That’s what I’ve heard. I’m excited to see it.”

Fizdale played Barrett 37.4 minutes per game in the preseason. He averaged 15.8 points, 3.3 assists and 6.7 rebounds. He shot 46.3 percent overall and even his 3-point shooting — his major weakness — was not horrid at 33 percent. He’s the Knicks’ best hope of turning into a star and his rookie year will be intensely dissected.

After a modest free-agent haul, the Knicks are not being picked for the playoffs in almost all projections. Barrett doesn’t mind being overlooked. In fact, he didn’t get one vote to win the rookie of the year honors in the league’s annual GM survey.

“We pride ourselves on having a bunch of dogs,’’ Barrett said. “We’re underdogs, we know that and we love that challenge.’’

With his buddy Zion Williamson felled for perhaps two months after surgery to repair a torn meniscus, Barrett could find himself heavily in the rookie of the year chase. He certainly will put up numbers as a starter, especially if Fizdale continues to roll with him for heavy minutes.

Barrett has made contact with Williamson, who was his roommate at Duke last season when the two carried the Blue Devils to the Elite 8.

“Of course, I’m sad when anyone goes down, but especially my boy,’’ Barrett said. “I hope he can get back healthy as quick as possible. I texted him [Monday] just making sure he was OK. He was in good spirits, so it was good.’’

In the preseason, Fizdale spotted Barrett at point guard for a bit because of his play-making abilities. If all of the Knicks’ point guards flame out, that’s where he could wind up, even temporarily for the season opener as Fizdale may shuffle the backcourt after center Mitchell Robinson’s injury.

The most important test comes Wednesday. TNT’s Stan Van Gundy takes preseason numbers with a grain of salt sometimes because teams don’t game plan against new players such as Barrett. Now they do.

“Basketball is fun,’’ Barrett said. “ It’s what I love to do. You got to have fun with it.”

For more from Marc Berman, listen to this episode of the Knicks podcast, “Big Apple Buckets”: