At the Stewart Hotel in midtown Manhattan, Shakur Stevenson shadowboxes from his seat, throwing punches in a flurry as if no one else is in the conference room.

"I'm just so used to it,'' Stevenson said. "It keeps me on my toes.''

Stevenson could be in a supermarket, in the mall, or walking down the street, when he involuntarily starts flicking jabs and uppercuts. The 20-year-old Newark native was never far from that zone as we talked last Wednesday about his transition from Olympic silver medalist to professional boxer.

"I know when I get in the ring with somebody else, no matter how good they are, I'm on a different level skillfully,'' he said.

He was on "a different level" three days later as part of a Top Rank-promoted card on ESPN at the Theater at Madison Square Garden. Stevenson dominated Oscar Mendoza on Saturday, winning his featherweight bout by TKO in the second round.

"Y'all still didn't see the best of me,'' said Shakur, standing in the ring. "Keep watching.''

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We will. He's 4-0, with two knockouts, in his dream job, his passion. It's all he's ever wanted to do since his grandfather, Willie "Wali" Moses, showed him how to box at age 5. Moses has been there the whole time, training him, watching him check off each milestone in his blossoming career.

"I would always say to him, 'Man, don't let me believe in you more than you believe in yourself' and he doesn't fall short on that self-belief," Moses said. "His dedication to himself and his craft is insurmountable.''

To Stevenson, boxing is everything. His love for the sport is what basketball is to NBA legends like LeBron James, Michael Jordan or Kobe Bryant. Stevenson most identifies with the inner drive of Hall of Famer Allen Iverson, when the hoops star said, "I play every game like it's my last game.''

Stevenson has the same mindset, so his transition to the pros has not been difficult.

"I fight every fight like it's my last fight,'' he said.

While most new boxers begin their career with four-round fights, up from the three-round bouts of the amateur level, Stevenson told his promoter, Top Rank, that he wanted to debut at six rounds.

"I'm not going to get nothing out of four rounds and lesser opponents,'' he said.

In the ring, he's making adjustments, realizing pace and patience are a must as he builds his endurance. He's quite aware that he doesn't fight as frequently, so he has to make each outing count.

"In the pros, you get one time, you get one performance,'' he said.

Stevenson is hard on himself, grading his early body of work as a C+. "I haven't peaked yet,'' he said.

That will come with more fights, when his man strength kicks in to fill out his 126-pound, 5-foot-8 frame.

"I've just got to stay focused and hungry,'' he said.

Putting in the work has never been a problem. In preparing for the Saturday fight, Stevenson sparred 12 rounds against Vasyl Lomachenko, the WBO junior lightweight world champion.

Stevenson described the experience as "amazing'' with the two-time gold medalist, who showed him why he is considered one of the best pound-for-pound fighters.

"I know that if I can get in there with one of the best boxers in boxing and handle myself, I can handle myself with anybody in boxing right now,'' he said.

Lomachenko, who retained his title Saturday at the Theater at the Madison Square Garden, said Shakur "has a lot of places where to grow, and I think he's going to be a very good prospect.''

As a young lion in the game, Stevenson is eager to be a headliner, like Lomachenko, preferably in Newark. Anthony Carr, a boxing trainer for 30 years in Newark, has watched Stevenson since he put on the gloves and likes what he sees now: good ring generalship, high boxing I.Q. and craftiness. He's a "gym rat,'' who wants to learn and get better, Carr said. "I think one day he'll wear that belt."

Antonio Leonard, a co-promoter for Stevenson, said he has a gift on par with former great fighters such as Roy Jones and Floyd Mayweather. "I see a lot of stuff happening for this kid,'' Leonard said. "He embraces everything."

His talent shines as brightly as his future, but Stevenson is down to earth, personable and humble.

"I know God put everything in front of me for a reason,'' he said. "He wouldn't put me in a certain position if he thought I couldn't handle it."

He's a mature young man with a megawatt dimpled smile, adapting to everything coming his way. Two weeks ago, he moved into his own apartment in Alexandria, Virginia, where he trains with his coach, Kay Koroma. The responsibility is quickly setting in.

"I have to pay my own bills,'' he said. And answer e-mails more regularly, something he said his idol, retired boxing champion Andre Ward, gets on him about.

The oldest of nine siblings, Stevenson is grounded by his family, whom he misses. He misses Newark, too, carrying the city with him into the ring. In bold capital glittering letters, "Newark" was emblazoned on the waistband of his red- and-white trunks and the bandana around his head on Saturday.

"I want to give a big shoutout to Newark, N.J. Without them, I wouldn't be who I am,'' he said in the ring.

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Angie Jackson, who works behind the scenes for Top Rank, calls Stevenson a "breath of fresh air,'' unlike many fighters she's seen during 40 years in the business.

"He's happy to go out there and do whatever he needs to do to promote himself. He knows he has to earn it,'' Jackson said.

That's what he did after we talked on Wednesday. Stevenson had to be at the Mendez Boxing gym for a 12:30 p.m. workout in front of boxing media outlets. On the way, a school bus was blocking the Chevrolet Suburban that Stevenson was riding in.

Instead of waiting, Stevenson jumped out on East 26th Street to walk the last block, signing an autograph for a fan in front of the gym entrance. He dashed down the steps and began answering questions from a horde of media waiting for him, Lomachenko, Guillermo Rigondeaux, a two-time Olympic gold medalist and junior featherweight champion; and Michael Conlan, an Olympian from Ireland. All of them fought Saturday night at the Garden.

Stevenson's comfortable now with the media. He took pictures, smiled, socialized, then left after 90 minutes and walked back to the hotel.

When I first wrote about him, in 2013, I said he was a keeper, someone who would be on the Olympic podium in 2016.

I asked him what we should expect of him in the next three years.

"People will see me with a world title,'' he said.

Barry Carter: (973) 836-4925 or bcarter@starledger.com or

nj.com/carter or follow him on Twitter @BarryCarterSL