When Michael Moorer returned to the Wild Card Boxing Club to serve as Freddie Roach’s chief assistant trainer two months ago, the retired former heavyweight champ knew he was home.

Moorer, one of the dozen or so world titleholders spawned from the Kronk Gym, says the atmosphere at the Wild Card is very similar to the famous but now-defunct Detroit gym.

There are many similarities but the main ingredient that links to the two gyms, according to Moorer, is the constant hard sparring between world-class fighters and young boxers who want to become world class.

“The wars,” is how Moorer put it. “You have wars in here. Your manhood is tested in the ring. That’s what makes you a fighter.

“I told a young fighter recently — a good kid from Minnesota I was working with named Joey Able — you need to go where your manhood will be tested. Kronk is gone, so now Wild Card is the place.”

That might explain why Jorge Linares, a Venezuelan junior lightweight titleholder based in Tokyo, was at Roach’s Hollywood, Calif. gym Thursday afternoon.

Linares, training in Las Vegas for a May 9 title defense in Texas, heard that Pacquiao began sparring this week in preparation for his May 2 showdown with Ricky Hatton and needed quality partners.

Urbano Antillon, the local fighter hired to be Pacquiao’s chief sparring partner, was out sick this week. Antillon’s trainer Rudy Hernandez told Linares, who, eager to fill-in for the tough lightweight contender, told his Las Vegas handlers to take him to Los Angeles immediately.

It might sound a little crazy that Linares would make a four-hour drive just to engage in one four-round sparring session, but the 23-year-old boxer knows, like Moorer, that there’s no better way to test his mettle than to get in the ring with the best fighter in the world.

Thursday wasn’t the first time Pacquiao and Linares have sparred, but it was the first time in many years. The last time they met in Wild Card’s ring, Pacquiao had just gained recognition as the linear featherweight champ by dominating Marco Antonio Barrera; and Linares was an unknown teen-aged featherweight prospect.

However, the young Venezuelan’s uncanny poise, balance, speed and accuracy forced the emerging Filipino icon to operate at 100 percent during their heated, head-turning gym sessions.

Now Linares, who won a title at featherweight before grabbing a belt at 130 pounds, is a full-grown junior lightweight with the frame of a junior welterweight. He’s added power to his finesse game, but Pacquiao, who advanced from junior lightweight to welterweight last year, has added considerable strength to his speed game.

Before Linares stepped inside the ropes, Akemi Irie of Teiken Promotions, told Roach that the lad had not sparred since sustaining a cut over his right eye while training in Tokyo last month.

“That’s OK,” Roach said. “Manny just started sparring Tuesday.”

Hernandez, who was there to work Linares’ corner during the sparring session, shook his head.

“Don’t they know there are no excuses in Southern California gyms?”

GYM WAR

At the sound of the bell, Pacquiao and Linares cautiously circled each other, showing a level of respect they seldom have to show to other fighters. Linares broke the tension by stepping forward with quick sharp jabs that Pacquiao avoided with quicker head and upper-body movement.

A minute into the round, Pacquiao exploded without warning, counter punching with lightening-bolt shots over and under Linares’ jab. The taller, rangier Venezuelan was knocked off balance more from surprise than sheer impact of the punches, but he quickly steeled himself and doubled a hard jab to earn respect and gain an opportunity to get his feet under him.

Linares got a second reprieve but no respect from Pacquiao, who tapped the younger man’s body while advancing forward. Neither fighter let his hands go with abandon in the final minute of the round, knowing that one mistake could result in catching a head-buzzing shot or even a knockdown. However, everyone in the gym could tell that the sparring session was heating up.

“I don’t want him to stand in front of Pacquiao,” said Irie, a U.S. representative of Linares’ Japan-based promoter. “I want him to move — in and out, side to side — like he does so well, but fighters always have their pride. They want to fight.”

Pacquiao asserted himself in the second round, increasing his pressure and playfully taunting the serious young man in front of him.

“Come on! Come on!” he barked as he advanced behind a high guard, slipping and blocking jabs as he worked his way in close enough to punish Linares’ lean torso with body shots.

Linares retaliated with a hard left-right combination to Pacquiao’s body.

“Double that jab on your way in! Double it!” Moorer reminded Pacquiao from ringside. “Hands up!”

Pacquiao listened but he continued to goad Linares as he pressed him.

“Go! Go! Let ’em go!” he said as he forced a bewildered-looking Linares to give ground.

It was obvious that Pacquiao had become a lot bigger and stronger than Linares recalled from their last sparring session.

Between rounds, Hernandez let Linares know in Spanish that it was time to “man up,” but he cautioned the titleholder to do so intelligently.

With fire in his eyes, Linares began the third round with a perfectly timed lead right that snapped Pacquiao’s head back.

Pacquiao immediately jumped in Linares’ chest and swarmed him with the kind of hard, power-punch combinations that he uses to end real fights. And then as suddenly as he turned on the rampage, Pacquiao turned it off and stepped back before the sparring session became too personal.

“Come on!” he yelled as he stepped back. “Come on! Jab, punch, do something.”

Linares, to his credit, did something. He landed a flush uppercut that once again jacked Pacquiao’s head back.

This time Pacquiao just smiled.

Linares went back to shooting a hard jab while stepping to his left. Pacquiao stalked him while blocking most of the jabs, letting his hands go in two- and three-punch combinations from various angles when he got in close.

Both fighters made statements in the third round, which made it very interesting going into the final round.

Pacquiao did not allow Linares to score first at the start of the fourth round. He charged Linares into the ropes and mugged him with punches once again. This time, however, Linares covered up and remained composed.

When Pacquiao let up for a second, Linares calmly timed a hard jab that landed flush and knocked Pacquiao back on his heels.

Before Pacquiao could even flash a smile, Linares launched himself off the ropes and nailed the pound-for-pound king with a clean one-two combination that was caught by HBO’s “24/7” film crew, which had been setting up production during the first three rounds of sparring.

Pacquiao jumped back in close with Linares and let go with a series of rapid-fire blows that forced the sharp-shooter into the ropes once more. Pacquiao didn’t land all of his power shots but he imposed his will on Linares before the talented Venezuelan landed a double right hand that landed with authority at the sound of the bell.

Pacquiao stopped himself in mid-punch. Turned and walked to his corner where Roach took out his mouthpiece and pulled off his headgear. Moorer stared at Pacquiao with a strange look of spacey satisfaction. Perhaps he was remembering his own gym wars, 20 years ago at Kronk.

Oscar Gonzalez, a 14-year-old amateur boxer Hernandez brought to the Wild Card to witness the sparring session, was still in awe as Pacquiao walked across the ring to give Linares a hug and thank him for the work.

“That was intense,” said Gonzalez, the younger brother of former WBC featherweight titleholder Alejandro “Cobrita” Gonzalez.

If Gonzalez wants to follow in his older brother’s footsteps, he’ll have to test himself in his own gym wars one day.

GYM NOTES

Max and Sam Garcia, the father-and-son team that train unbeaten (13-0-2, three KOs) junior lightweight Eloy Perez, were at the Wild Card before Linares and Pacquiao’s sparring session.

They say the skilled Salinas, Calif.-based prospect might co-headline a May 8 card with Robert Guerrero in nearby San Jose. The Golden Boy Promotions card would be televised by ESPN2 and could be held at the HP Pavilion or at the cozier Civic Auditorium.

Linares (26-0, 17 KOs) will make the first defense of his WBA 130-pound title against Mexico’s Josafat Perez (12-1, seven KOs) in El Paso.

Hernandez believes that Teiken-promoted Koji Sato (14-0, 13 KOs), a hard-hitting 160-pound prospect who was once trained by hall-of-famer Mike McCallum, has a puncher’s chance to upset WBA middleweight titlist Felix Sturm when the two meet in Germany on April 25.

Speaking of punchers, 50 miles south of Hollywood in Costa Mesa, Calif., Linares’ countryman and former stablemate Edwin Valero finished up his third week of training with new trainer Robert Alcazar.

Valero looked sharper than ever working 10 hard rounds with Alcazar at the Orange County-based kickboxing facility where they’ve set up camp.

The speed and power he exhibited defies description.

Valero’s April 4 opponent, Antonio Pitalua, better be the toughest S.O.B. on the planet if he hopes to go more than three rounds.

Doug Fischer can be reached at [email protected]