When the man known around the NBA as the dunk guru is blown away by your skills, you might be ready for a breakout performance on the national stage. 

Chuck Millan worked with Jericho Sims last week in Tarrytown after the Knicks’ big man was added as one of four contestants for the NBA Slam Dunk Contest on Saturday night at All-Star Weekend in Salt Lake City. 

Millan, a former professional dunker and the CEO of Team Flight Brothers, believes the showcase competition could make for a coming-out party for the 6-foot-10 Sims due to his freakish jumping ability. 

“People are definitely gonna be wowed by him. He’s coming right out of the gate with some stuff that hasn’t happened before. If people don’t know who Jericho Sims is, they’re gonna know on Saturday night who he is,” Millan told The Post in a phone interview Friday. “What I can say is I’ve been in the dunk business for 20 years now, whether it’s the professional dunkers or NBA guys. Jericho, anything you’ve seen of him, you have no idea how high this kid can really jump. 

“I can honestly say it is the highest I’ve ever seen anyone get over the rim in my life. And that’s saying a lot. I’ve seen Vince Carter in his prime going to the top of the backboard. Jericho has a couple of dunks that have never been done before.” 

Sims, whose 44.5-inch vertical leap was the third-highest recorded in the history of the NBA Draft combine in 2019, was a late addition to the field as a replacement for Portland’s Shaedon Sharpe. The Knicks’ second-year center will compete with Kenyon Martin Jr. (Rockets), Mac McClurg (76ers, G-League) and Trey Murphy III (Pelicans). 

Millan has worked with all four players on their dunks and described them as having “four different dunking styles.” The 24-year-old Sims recently was seen in a viral video with his head above the rim 

“Yeah, he can get his shoulder on the rim, and he can do that whenever he wants. It’s crazy,” Millan said. “I’ve seen guys with the vertical that he has, 45-46 inches of vertical, but never on somebody that’s 6-foot-10. 

“It’s a huge difference. When he jumps as high as he can, and does some of this stuff he can do, I think the crowd is going to react more so, like, not going crazy, but, like, in shock. Like, what just happened? That’s how we’ve all reacted. Like even the NBA production crew was like what the hell was that? It’s been pretty cool to see for us, and this is what we do every day.” 

The 39-year-old Millan has tutored several past dunk champions, including Sims’ teammate Obi Toppin, who won the contest last year to join Kenny Walker (1989) and three-time winner Nate Robinson (2006, 2009, 2010) as the only Knicks to win that title. Toppin even executed one of his winning dunks with a leap over Millan. 

Toppin declined to participate this year, Millan said, in part to give Sims the opportunity to compete. 

“Obi was pretty adamant about that. He initially was leaning towards doing it, but he was like, if I pull out, will my teammate get a chance?” Millan said. “And it ended up working out that way. 

“But also, Obi has not written off dunk contests in the future. I think Obi is waiting for his brother to get to the league, and then they can kind of have a brotherly showdown at All-Star weekend.” 

Toppin’s younger brother, Jacob, is a senior forward at Kentucky, averaging 11.9 points per game. 

Millan played what he described as “minimally” as a college player at Sacramento State two decades ago, and he initially took a job at Nike in brand activation doing dunks at events in Asia and Europe. His company provides dunks for halftime shows across the league, and the NBA officially has made him available to work with dunk contest participants since 2018. 

Past winners, such as Terrence Ross, John Wall, Donovan Mitchell and Derrick Jones Jr. also have credited Millan with their dunking success. 

“This,” Millan said, “is my Super Bowl, man.”