Zab Judah has always been known for his boxing skills. It was his punch, however, that scored him the biggest win of his career Saturday night.

The Brooklyn native shocked hometown hero Cory Spinks with a determined power display, scoring a sudden 9th round technical knockout to win the undisputed welterweight championship before an electric crowd at St. Louis’ sold-out Savvis Center.

Judah dropped Spinks late in the round with a flurry of straight left hands. The defending champion got to his feet, but was swarmed by a challenger eager to resurrect a sagging career. After Judah pleaded with referee Armando Garcia to stop the fight, Garcia finally intervened at the 2:49 mark as the former junior welterweight star scored the first big upset of 2005 and turned the suddenly-interesting welterweight division upside down.

“I was determined and I was hungry,” Judah told Showtime’s Steve Farhood afterward. “I know Cory Spinks is a great boxer, and he got an edge on me in the middle rounds. But I knew I had to knock him out.”

Judah had previously been disappointing in big fights, losing to Kostya Tszyu via knockout in 2001 and to Spinks via decision last April. But he silenced the critics, showing patient aggressiveness in finally achieving his awesome potential.

Now he sets himself up for  possible big money fights against a host of big-name challengers, namely Oscar De La Hoya and Shane Mosley, who are both reported to be dropping back down to 147-pounds.

And a Judah-Tszyu rematch suddenly looks like an intriguing proposition.

Tszyu knocked Judah out in the second round in 2001, and Judah was sharply criticized afterwards for his boorish in-the-ring behavior. But against Spinks Saturday, the man known as “Super” showed he had grown up in the last four years.

Judah knocked Spinks down in the final round of their first fight, and vowed to pick up where he left off. He did just that, staying flatfooted virtually the entire fight and chasing after the fleet-footed champion to get an early lead.

Spinks used his jab and movement to provide Judah with some problems in rounds four and five, but Judah continued his aggressive game plan. It began to pay big dividends in round seven, when Judah dropped Spinks with a left hand just after the bell sounded to end the round.

Finally, in round nine, Judah connected with another straight left that staggered Spinks and a follow-up left put him down. He rose on unsteady legs, and Judah looked like Tszyu himself in pursuing his hurt foe. A series of punches left Spinks defenseless, and Judah looked to Garcia twice to stop the fight. A series of punches capped by another left convinced Garcia that Spinks had had enough.

Judah’s puncher’s approach paid off on the scorecards as well, as “Super” led on the tallies of judges Tom Kacszmarek (77-75), Gary Merritt (79-73) and Joe Pasquale (78-74).

Judah’s record improves to 33-2 with 24 knockouts and one no-decision. Spinks falls to 34-3 with 11 knockouts.

As for Spinks, the now-former-champ’s shaky chin appeared to be his downfall. Showtime’s Al Bernstein likened the upset to James Toney’s 1991 stunner over Michael Nunn for the IBF middleweight title in Nunn’s hometown of Davenport, Iowa.

Spinks, who earned $1.2 million to Judah’s $100,000, was classy in defeat.

“He caught me with a good shot,” he said. “I felt like I could have continued. I hope (he gives me another fight).”

Promoter Don King said a third Judah-Spinks fight is a possibility, exaggerating just a tad in calling the series the “Ali-Frazier” of the era. Either way, Judah seems primed to cash in on a career that is suddenly red-hot.

And Judah showed a human side with his plea to Garcia to stop it.

“I didn’t want to hurt him,” Judah told Showtime. “I saw his eyes rolling around in his head. I have a great deal of respect (for Spinks). He has a wife and children. I was looking at the ref like, ‘What are you doing?’”

In the main support to Judah-Spinks 2, heavyweights Monte Barrett and Owen “What The Heck” Beck put on a thrilling slugfest before the veteran Barrett emerged with a 9th round TKO.

Barrett overcame a nasty cut over his left eyelid to knock the gutsy Beck down three times – twice in the final round. Like Judah, the two heavyweights sat on their punches and brawled to the delight of the throng on hand.

Barrett took advantage of Beck’s habit of dropping his hands, connecting with enough power punches to convince referee Jay Nady to stop it at 2:52 of round nine.

Barrett improves to 31-3 with 16 knockouts. Beck suffered his first loss in dropping to 24-1 with 18 knockouts.