PHILADELPHIA -- For a few special months, Hasim Rahman was the heavyweight king, cheered by boxing fans and wooed by greedy promoters. As improbable as it was, his one-punch knockout of Lennox Lewis gave the world a refreshing new heavyweight champion.

Barely two years later, Rahman's championship days are now only a hazy memory. He fights Saturday night against David Tua hoping to salvage his career, but ready to hang the gloves up if he can't win.

"If I can't win this fight, there's no need to go on,'' Rahman said. "I don't want to stop yet, but if I lose I'm going to call it quits.''

There's a lot at stake for two big-punching heavyweights in the 12-round elimination fight. The winner will be in line to face IBF champion Chris Byrd, while the loser can either retire or begin climbing the ladder once again.

The fight (10 p.m. ET, HBO) is a rematch of a disputed 1998 fight that Rahman was winning until Tua wobbled him with a shot after the bell ending the ninth round and then stopped him in the 10th.

At the time, both fighters were up-and-coming heavyweights. Now, they're both in need of a big win to keep going.

"He cheated,'' Rahman said. "I beat him easy. Why wouldn't I beat him again?''

Nor surprisingly, Tua doesn't quite see it that way.

"I'm accepting of the fact of what happened then,'' Tua said of the first fight. "It's the same guy this time, but he's a different fighter and it's a different day. The past is the past.''

Tua has built a career on knockouts like his dismantling of former champ Michael Moorer, which came with a left to the chin and ended their Aug. 17 bout after just 30 seconds.

Like Rahman, he has fought Lewis, though he gave an uninspired effort in his only title fight and lost a lopsided unanimous decision.

Rahman's one-punch knockout of Lewis, meanwhile, stands as one of the biggest upsets in boxing history. Rahman's crushing right to the head in the fifth ended the fight, giving the then-unknown Baltimore heavyweight instant fame and riches.

But it's been a hard road since. Rahman's reign lasted only seven months, before Lewis reclaimed his titles in a rematch with a one-punch knockout of his own in the fourth round.

In his only fight since, Rahman (35-4) was stopped last June by Evander Holyfield, suffering a grotesque forehead hematoma from a head butt, which prompted an eighth-round technical decision for Holyfield.

"Rahman has to be the luckiest guy in boxing,'' Tua trainer Kevin Barry said Thursday. "Four fights ago, he was struggling to beat Frankie Swindell. In his last fight, he made an old Evander Holyfield look young and he's coming off back-to-back losses.''

Tua, 30, of South Auckland, New Zealand, isn't making any predictions.

He wouldn't talk about his strategy, except to say he will be the aggressor.

"When you're fighting David Tua, you have to be prepared because I'm going to be right there in front of you the whole time,'' said Tua, who will make $1 million, to Rahman's $750,000.

Byrd, who will face the winner, favors Tua (42-3).

"Rock outboxed him the last time and he still lost. If Rahman can keep his composure and last 12 rounds, he'll have a chance, but you have to go with Tua,'' said Byrd.

The fight, which is the co-feature of the Bernard Hopkins-Morrade Hakkar middleweight championship card at First Union Spectrum, has more implications than the main event.

In the 12-round main event, Hopkins (41-2-1) will be making his 16th consecutive title defense. The fights will be televised by HBO, beginning at 10 p.m. ET.