When he's on top of his game, you'll find Zab Judah (36-6, 25 KOs) using his lightning-fast hands to dismantle world-class opponents on HBO or Showtime cards.  But when he's slumping, you'll find Judah exactly where he'll be on Saturday night when he faces the untested Ernest Johnson (18-2-1, 7 KOs):  on the undercard of a pay-per-view bout he has the talent to be headlining.

Judah, 31, is no stranger to being the opening act.  Four-and-a-half years ago, he narrowly defeated 38-year-old journeyman Rafael Pineda on the undercard of the first rematch between Roy Jones Jr. and Antonio Tarver.  Five months later, he obliterated Wayne Martell in a first-round knockout under the Felix Trinidad-Ricardo Mayorga slugfest.  And in May of 2005, he blitzed Mexican Cosme Rivera via third round TKO below the Trinidad-Winky Wright duel.

HBO bigwigs are always happy to give Judah a prominent stage for his first comeback fights because “Super” looks good – damn good – thrashing lesser opposition.

But over the better half of the past ten years, “looking good” has been precisely Judah's problem.  He's spent far too much time tuning up on lesser opponents.  These skill-sharpening fights are a result of Judah's countless blown opportunities.

Judah was one of the sport's hottest prospects in 2001 when he was caught by a lethal Kostya Tsyzu right hand that sent him wobbling around like a drunken college frat student after a Saturday night party en route to a second round knockout loss.  But prospects – especially those as talented as Judah – are entitled to at least one defeat, no matter how devastating.

So Judah got back on his horse and won three straight fights against solid opposition.  But when he moved up from 140 pounds to challenge 147-pound titlist Cory Spinks, he again blew a big chance, this time not throwing enough punches en route to a unanimous decision loss.

Judah again rebounded with wins against decent opponents, Pineda and Martell, before exacting revenge on Spinks in the pair's rematch, which made Judah the undisputed welterweight world champion.

Just two fights after the career-best win, however, Judah lost a unanimous decision to the unheralded Carlos Baldomir.  The reason for the defeat (according to Judah):  lack of proper training.

So it came as a big surprise to the boxing world when it was announced that Judah would be facing then pound-for-pound king Floyd Mayweather Jr. just three months after the Baldomir defeat.  Nobody gave Judah much of a chance considering he had just lost to an unknown Argentinean, but Judah went into the bout with the same confidence he carries around when projecting machismo in the streets of Brooklyn.

 Judah started the bout brilliantly, beating the fast Mayweather to the punch and bullying “Pretty Boy” around the ring with sharp rights and robust lefts.  Mayweather, used to making opponents look silly, was clearly frustrated by Judah's skills, and after five rounds, Judah was widely ahead on judges' scorecards.

But again, Judah blew his chance at making history.  Around the sixth round when his get-go energy began to run out, Judah gave in to Mayweather's peppering combos.  Instead of firing back, Judah succumbed to Mayweather's fast hands.  Judah refused to dig down deep, and he lost a decision because of it.

Since the Mayweather fight, Judah has lost to Miguel Cotto (June, 2007) and Joshua Clottey (August, 2008) and won a few tune-up bouts in between.  Although Judah fought valiantly in his loss to Cotto, he essentially quit against Clottey, indicating that he couldn't see out of a cut on his eye which was opened from a Clottey combination.

So here Judah is again, building himself up for another potentially-big opportunity.  He should have no problem handling Johnson, whose best opponent has been fringe contender Ernesto Zavala, but will a win really mean anything?  We'll only know if Judah can take advantage of his next chance – if he's not out of chances already.