ATLANTIC CITY – Michael Moorer is a two-time world champion, a 34-year-old past his prime who abused his body the way he once abused foes. David Tua is a title contender trying to scale the mountain Moorer fell from, using the sport’s hardest punch and one of its toughest jaws.

The two friends faced off last night at Trump Taj Mahal, as part of HBO’s “Boxing After Dark” series. The winner could be a step away from hoisting a championship belt, while the loser might be a misstep away from club fighting.

“David is one of the biggest underachievers in the heavyweight division. Everybody’s seen him, sees the skills, and expects so much from him. He should’ve been heavyweight champion of the world by now,” said Kevin Barry. And that admission came from Tua’s own trainer.

The 10-round tilt was billed as “Everything on the Line,” and indeed it was. In the watered-down division – there’s WBC/IBF champ Lennox Lewis, Wladimir Klitschko, and guys like John Ruiz and Chris Byrd, and not much else – why wouldn’t last night’s winner deserve a shot?

The heavily favored Tua (40-3, 35 KOs before last night) was ranked third by the IBF, and has some good wins. The 29-year-old TKO’d former WBC/IBF champ Hasim Rahman, TKO’d then-unbeaten Fres Oquendo in his last fight and KO’d WBA champ Ruiz in :17 here in Atlantic City in ’96.

But the 5-foot-9, 243-pound Tua has come up short in big bouts. Lewis used his jab to dominate Tua in 2000, and Byrd was too elusive last Aug. 18. His left hook is vicious and jaw vaunted, no part of his body has touched the canvas except his feet. But skilled men have given him fits.

“I know it’s a dark cloud that follows him around. But I give him all the credit. He’s a world champion and I’m not,” Tua said. “He’s used that and turned that around. He’s gotten better and better. Since that fight he’s gone up and up and up. He’s making money and getting paid, and he’s winning, so my respect goes out to Ruiz.”

Moorer (43-2-1, 34 KO’s) has never stayed focused for long, frustrating trainer Teddy Atlas into quitting and eventually taking three years off to drink and party and balloon to 270 pounds. But he’s spent 10 weeks in Detroit with Emanuel Steward, weighing in at 224.

“The winner of this fight is going to have a number of opportunities; certainly a match against Klitschko is one of them,” said Kery Davis, HBO Sports’ Senior VP of Programming.

“But also the winner might be in line for another shot at Lennox, especially if it’s Moorer, who’s the only great fighter of Lennox’s era who Lennox hasn’t fought. He was the one guy who held the heavyweight title that Lennox hasn’t fought.”

That’s if the Brit, who’s been making noises about hanging up the gloves, doesn’t retire. If he does, Tua could face Chris Byrd for the vacated WBC/IBF titles. Tua earned $500,000 last night and Moorer $400,000; the winner stands to make triple-figures in his next fight.

Last night, half-a-million. A title shot? Priceless.