DURHAM, N.C. — If the kids in the student section weren’t exactly nervous yet, the first 17 minutes of the game had them muttering in between their clever chants. St. John’s had beaten Duke last year mostly by pushing the Blue Devils around, by out-toughing them at Madison Square Garden. Zion Williamson wasn’t at that game.

But he knew all about it.

“This is the Duke brotherhood,” he said with a grin. “People on one team know all about what happened on other teams, what they went through.”

The grin widened into a smile.

“We knew this would be a physical game,” the Duke forward said. “We were ready.”

At one point, Marvin Clark II laid out Duke’s Cam Reddish — a hard, clean foul in any gymnasium in America except Cameron Indoor Stadium. Here, it was called a Flagrant I. Here, Duke coach Mike Krzyzewski seized on the moment to shed his suit jacket and yell at his players: “YOU GONNA LET THEM DO THAT TO ONE OF YOUR PARTNERS?”

“No, sir,” Williamson said. “No, sir.”

Still, the Johnnies counter-punched. With three minutes to go in the half, it was 35-33 Duke, and Shamorie Ponds was dribbling upcourt … until Tre Jones stripped him clean and drove for a layup. That was bad news for the Johnnies. The worse news was this:

It wasn’t only Cameron that was fully electrified now.

Zion was, too. The final 2 minutes and 41 seconds for Duke read this way: Zion layup, Zion offensive rebound, Zion layup, two Zion free throws, Zion 5-footer, Zion steal, Zion dunk. That’s a one-man 10-point run.

You can be the toughest basketball team in the world. You can be tougher than old Chuck Bronson on the subway. And it doesn’t seem to matter in 2019 as long as Williamson chooses to shift his gears to a level with which only he is familiar. Good luck sharpening your elbows, setting your feet and getting in his way.

“When he plays like that,” Jones said, “you almost don’t want to play. You almost only want to watch. It’s amazing.”

There will be time plenty to scrutinize him and second-guess what you think about him. Yes, his outside shot is uglier than a Nick Nolte mug shot. Yes, he is that rare person who looks smaller in person than he does on TV. Yes, he will have a long challenge ahead of him replicating all of this against the grown men who stuff NBA rosters.

But, damn, is he ever fun to watch in the here and now.

Unless you have to, you know, guard him. Then nothing about it is fun. Williamson hit 13 of his 17 shots Saturday (even swishing one of his three 3-point attempts). He scored 29, had two blocks and added five steals for kicks and giggles. St. John’s was feisty for 17 minutes. The Johnnies were flattened 91-61 across 40.

“Actually, I was looking forward to it,” said Clark, who certainly proved that he wasn’t going to be intimidated, who along with Mustapha Heron and LJ Figueroa seemed very much at home in a hostile, high-octane house. “We’ve all heard stories about him, he’s a freak of nature. It’s crazy seeing it live, though. He’s a mammoth of a man.”

(A word about the Johnnies: The very best of who they are was on display for most of that first half, even with Jones shutting down Ponds completely. Krzyzewski declared them an NCAA Tournament team but with a caveat: “They have to win some games like everyone else.” If they can bring those first 17 minutes with them the rest of the season, they really could be OK.)

Williamson isn’t blind and he isn’t deaf to the hype around him. He wouldn’t admit to seeing The Post’s back page Friday that featured him, Kevin Durant and Kyrie Irving in Knicks uniforms, but he did say, “It would be dope to play with KD and Kyrie.” And specific to Knicks fans he said, “I appreciate the love, them wanting me to come to that team.”

But he added what has become a staple of his remarks every time he faces a bank of notebooks and microphones: “You do think about it. But this is also the only time I’ll get to experience college. I’m enjoying the experience and don’t want to miss out on anything.”

Krzyzewski, smiling wryly, insisted he hasn’t followed the great Knicks purge, but he did say, “We have a couple of players here that might be targets. Hopefully, they still have some other players left, too.”

Whoever winds up with this one? That’s not a bad place to start.