Had you only seen the Irish middleweight John Duddy sparring in Gleason’s Gym, and never caught one of his pro fights, you wouldn’t give him a second look.

A couple of weeks before his Madison Square Garden debut on June 11, the prospect was eating jabs like it was Limerick Ham. The sparring partner doling out the abuse was not Winky Wright; he was no more than Golden Gloves material.

As sweat flew off Duddy’s headgear with each shot he absorbed, the Gleason regulars pulled their chairs closer to the ring for a better look. An old-timer in a frayed suit vigorously worked a toothpick between his teeth, while a heavyset trainer sitting beside him squinted as if he were staring into the sun. Fighters done with their work pantomimed slipping punches—the ones landing clean on the 25-year-old whose record stands 9-0 with 9 KOs (seven of them coming within the first round).

Could this really be the marvel from County Derry that everybody’s been talking about? Not only was it him; this disheartening display is a common occurrence.

“I think for Harry [Keitt], me trainer, and all the people working with me here,” explained Duddy, “it must be very frustratin’. I’ll try to do me best, I’ll try to learn, and it doesn’t seem to fall right for me.”

Although Duddy is one of the hardest workers you’ll witness at Gleason’s, he is the opposite of a “gym fighter,” a boxer who glitters during sparring but can’t put it together when it matters most.

Duddy’s transformation is so extreme he could be diagnosed with Split Personality Disorder; he’s a regular Dr. Jekyll and Mr. Hyde. (But don’t expect his handlers to check him into Bellevue anytime soon.)

“Before a fight, John grunts at me when I say hello,” said Duddy’s matchmaker, Jim Borzell.  Asked to explain more about these grunts, Borzell made a guttural sound that a creature might make. “Ggggrrrrrrr! Like that. He gets into a zone, a zone like you’ve never seen before. Comes out, blows his guy away, and then he’s Mister Happy again.”

This is exactly what happened last March 18 on St. Paddy’s Day. Duddy was taking a big step up in facing Lenord Pierre (at the time 16-0 with 11 KOs), and doing so as the main event on ESPN2’s Friday Night Fights. Pierre was summarily dispatched in 83 seconds, in a fierce fashion that recalled a young Mike Tyson. As fate would have it, Pierre’s trainer was Tyson’s chief second during his prime, Kevin Rooney.

“Kevin Rooney said to us, ‘I don’t know who your advisor is but you’re making a big mistake,’” said Duddy’s head trainer Harry Keitt. “A lot of people at the gym said, out of concern, ‘Why are you takin’ this fight?’ When they first offered the fight, I said no. Not because of Pierre’s record. I said ‘When John beats him, it’s gonna be hard as hell to get him fights.’ We tryin’ to stay under the radar.”

Too late for that. Duddy’s hyperkinetic knockout was the type of highlight reel stuff that puts a fighter on the map, and has the boxing industry and fans alike salivating for more. Mickey Ward, who was the guest host that night on FNF, proclaimed Duddy “the real deal.” Ward is a straight shooter who is not prone to making statements he doesn’t believe in his heart (not that he’d mind seeing a great Irish fighter on the scene).

When Borzell was first approached by Duddy’s manager/mentor Eddie McLoughlin, McLoughlin made the brash statement, “Put him in with anybody.” Borzell was the matchmaker for a card promoted by Sal Musumeci’s Final Forum Boxing. “I wasn’t attached to either fighter, so I took the opportunity to give the audience—which was my primary objective—a good show. This kid Terek Rached was a tough SOB. John blew the doors off him.”

While it is premature to make hyperbolic pronouncements about a fighter whose wins aren’t yet in double digits, one thing can be said of Duddy: He has not been matched soft. Borzell has put him in with several slick southpaws, and guys who like to bang. Saturday, on the undercard of Cotto-Abdullaev, Duddy is facing rugged, game journeymen Patrick Thompson (9-4-1).

“He’s very strong, durable, has a good right hand,” Duddy said of his upcoming opponent. “He’s easy hittin’. When I spar, I suppose I’ve been shown to be easy hittin’…” Duddy laughed. Thompson has fought several good fighters (Sechew Powell, Giovanni Lorenzo, Alfonso Gomez), and has only been stopped once. “I told Top Rank”—the show’s promoter—“we weren’t going short on it,” Borzell said.

Duddy had a long and accomplished amateur career, winning 100 fights and losing 30. In 2001, he lost a close decision (5-4) to Andre Ward, the sole American gold medallist in Athens. He had a reputation as a fine boxer but not a big puncher, stopping only a few opponents. So the awesome power he now displays comes as a shock to many, especially incredulous boxing writers back home. Duddy explained that the power might have always been there. His father, who was a pro boxer, always told him he hit hard when working the hand pads. They couldn’t understand why it didn’t translate in his fights. However, some of the most feared punchers of all time—Tommy Hearns and Felix Trinidad—did not demonstrate KO power as amateurs.

In 2003, Eddie McLoughlin threw at Duddy what he describes as “a lifeline.” McLoughlin offered to bring him over to New York and give him a shot at a pro career. To Duddy, New York is the center of the universe and Gleason’s is “the holy grail of boxing.”

By toiling away at Gleason’s Duddy has slugged his way beyond everybody’s expectations. He believes that the proper punching technique he’s learned there – sitting down on his punches, applying his full body weight behind a shot – along with a new mindset he’s developed – has helped surface a primal force in him.

Beware. Mr. Hyde will be on the loose this Saturday at the Garden.