-- In a large and loud and very hot makeshift gym at Nike world headquarters, Floyd Mayweather Jr. is working out. He throws phantom punches, checks his form. He looks in the mirror, but knows he can't look ahead. For arguably the best boxer in the world, it's hard not to.

Perhaps he sees Winky Wright. Or maybe Zab Judah. And in the background, there's Oscar De La Hoya. All big-time opponents, setting up the flashy and feisty new welterweight for a big-time payday.

But not yet. Saturday night at the Rose Garden in nearby Portland, Mayweather instead will see one of the more accomplished fighters of the last decade staring back -- Takoma Park native Sharmba Mitchell. The 12-round, 147-pound nontitle bout won't command the megabucks a matchup with Wright or Judah would, but it's another fight -- the first for Mayweather (34-0, 23 knockouts) since a six-round demolition of WBC 140-pound champ Arturo Gatti in June.

For Mayweather, 28, a three-time world champion many consider the finest pound-for-pound fighter in the professional ranks, the bout is just another step toward boxing immortality, the type of legend he admits he can only become once he faces -- and vanquishes -- the best of his peers.

"I'm not in this game to lose," Mayweather said, wrapping up a workout earlier this week. "I'm in it to win. I'm not in it for the money, but to be a living legend. I am a living legend."

He may not be in it for the money, but he has 3.75 million reasons to appreciate the challenge that Mitchell, seven years Mayweather's senior, will offer. Should he lose, it could cost much more.

Mitchell (56-4, 30 KOs), a former two-time world champion, making just his second start at 147 pounds, is more than just the easy foil, hardly an over-the-hill opponent. His southpaw style and veteran experience could give Mayweather a surprising challenge.

"He's giving me an opportunity, I'm giving him an opportunity," Mitchell said. "Us fighting each other is a great thing. . . . I just have to be myself and do what I do best. I never overlook everyone."

Mayweather can't say enough that he's not looking beyond Mitchell to bigger paydays. "I just stay focused. It's one man at a time. He's not used to fighting in arenas with 13,000-14,000 people. I am. I've been training like it's the last fight of my life."

On this day, there's not a terrible amount of training. As his adviser, Leonard Ellerbe, says, "Three days before a fight, if you're not in shape, you're in trouble." And Mayweather is in tip-top shape, in perfect form, wowing onlookers with a minute-long punching exhibition with his eyes closed.

There's a lot of money coursing through the leafy Nike campus, with buildings named after Michael Jordan, Tiger Woods and Lance Armstrong. Inside the Bo Jackson Sports Center, Mayweather is big money, too, one of the few lesser-weight fighters who can command a pay-per-view audience. The Las Vegas resident originally from Michigan, who recently re-signed with promoter Top Rank after their brief rift led to a lawsuit filed against the fighter, wanted to jump up in weight to face Wright at 154 pounds, but a proposed Nov. 12 bout fell through. Judah, at 147 pounds, also was a possibility, but the boxers' camps couldn't reach an agreement.

"It doesn't matter who I fight, I'm tired of calling names out in all these interviews," Mayweather said. But it's just too tempting. "I would fight Winky Wright. He didn't want to fight. Zab Judah didn't want to fight. Shane Mosley didn't want to fight."

Looming in 2006 is De La Hoya, the "Golden Boy," a perfect foil for "Pretty Boy" Floyd. It would be the biggest money bout in boxing if De La Hoya returned to the ring for the first time since he was knocked out by Bernard Hopkins in September 2004. It's a bout Mayweather thirsts for, with an added level of intrigue in that his estranged father, Floyd Sr., trains De La Hoya.

For now, Mitchell stands before the champ.

"It's going be a nice little duel, trust me," Mitchell said.

One man at a time.

"He can't say he's ever seen a fighter like me," Mayweather said. "You can't ask him, 'cause he won't know the answer till Saturday night."

Takoma Park native Sharmba Mitchell, left, and Floyd Mayweather Jr. will face each other tonight in a 147-pound nontitle bout. Mayweather hasn't fought since June.