LAS VEGAS — Mikel Brown Jr.’s pro debut showed he can make extraordinary plays. Now the Nets have to help him make the ordinary ones over and over.

Because once he does — once Brown gets big and strong enough for his body to catch up to his brain defensively — the Nets may finally have their building block.

“He’s an electric offensive player. His ability to make plays at the rim, in the midrange, from 3 is really impressive,” Nets summer league coach Dutch Gaitley told The Post. “The things that impressed me [were] his ability to rebound. For a guard to come back [from the perimeter] with that athleticism is really impressive. He was active defensively; he had deflections, he forced some turnovers.”

Brown’s summer league debut Monday was his first action since back woes ended his freshman season at Louisville in February. He showed elite passing and a sharp handle; now he and Egor Dëmin must figure out how to leverage their versatility as a weapon.

“The energy he came into the gym with and the goals he has for the team, not just for himself, that was very impressive … I really like to play with him. We can be very good together,” Dëmin told The Post.

“Now as the defense says, ‘Hey we can’t let this guy get in the paint: We’re going to blitz him or switch him’ — can he back the ball out and just make the simple one and let his teammate [score]?” Gaitley asked rhetorically. “[But] he makes the spectacular look easy. And that’s what he was able to do.”

For Brown to be as good as he can, the wiry rookie is going to have to add muscle and physicality.

“The thing we’re challenging him now is figuring out his spots in the flow of the offense. Him and Egor together, how can we get both of them going at the same time,” Gaitley said. “And defensively is increasing his physicality. The first part is hitting bigs when they’re rolling, boxing them out. He’s smart, so some of the stuff he’s doing defensively I told him was Level 4, Level 5. We’re still on 1.5 in summer league.

“He’s smart enough that he knows what the next iteration we may not get to until October; but he knows it already. How can we do the little things and the simple stuff perfect before we build on [it]? And the last part is just getting into the ball, more physicality, pick-and-roll, which defensively isn’t what he’s not known for right now, but it’s something that’s going to surprise a lot of people.”

It’s tough love and hard coaching that Brown welcomes.

“That dialogue is needed, because at the end of the day, I want to be a better player. And they want me to be a better player,” Brown told The Post. “So, to be able to take that accountability and take that feedback and apply it, it’s definitely what I’m going to do. Just being more physical, more consistently, is the biggest thing.”

Picked sixth, Brown went one spot ahead of high-scoring Darius Acuff Jr., his rival going back to their high school days.

That sparked endless discourse online and from talking heads. It’s bloviation that Brown ignored.

“People are going to say what they want to,” Brown said. “Me and [Acuff] already talked about this is the dream of ours. We were trying to predict where we were going to go and we called it. We both got it right. So me and him have that friendship, but we’re also very competitive. Once we’re on the floor, it’s a battle every time. But I don’t pay attention to that stuff. What’s meant to be is meant to be.

“We’re right where we need to be. I can’t wait to go against him for the rest of my life.”

After missing their summer league opener against Acuff’s Kings, Brown’s next chance to go against him will be Tuesday in Las Vegas.

“We’re very competitive. Once we’re on the court, we’re both killers,” Brown said. “That’s how it is every time we play each other.”