David Diaz realizes he might just be a speed bump on Manny Pacquiao's road to history. He's still determined to make that trip as rocky as possible Saturday night.

Diaz, the unlikely WBC lightweight champion from humble Chicago roots, is among the biggest admirers of Pacquiao's evolution from a 106-pound scrapper into a three-division champion who's attempting to move up for a historic fourth belt at the Mandalay Bay Events Center.

Pacquiao is a heavy favorite in the sports book and among most educated observers, who can't imagine Diaz standing up to Pacquiao's unparalleled combination of speed and power. Even if Pacquiao (46-3-2, 34 KOs) is a bit slower carrying five extra pounds, as Pacquiao trainer Freddie Roach suggests, it's tough to imagine Diaz trading 12 rounds of blows with the Filipino action hero.

Even Diaz isn't sure what chance he'll have against the Pac-Man. But after years of being underestimated, he's ready for another shot at the improbable.

"I just want it to be a war," Diaz said. "I want it to go down as one of the greatest fights of the century. If I come up on the short end of the stick, then so be it, but I want people to remember it."

Diaz (34-1-1, 17 KOs) also has defied expectations with much less fanfare than Pacquiao. Diaz took this formidable fight for the $850,000 payday that should help him to buy a better car than his 1991 Honda with no air conditioning, but also for the chance to test himself against the world's best.

After beating out Zab Judah for a spot on the U.S. Olympic team, and after winning his title through a stunning 10th-round knockout in a fight he was losing, Diaz has learned to believe in himself when everybody else discounts him.

"If I was Manny, I'd be concerned about the will that I have," Diaz said. "It's not going to be easy, if that's what he thinks. He's going to have to throw bombs and stay in there."

With a victory, Pacquiao would become the first Asian boxer to win world titles in four weight classes. He moved up to lightweight because he has precious few worlds left to conquer, with a long list of big paydays and epic victories over Mexican champions Erik Morales, Marco Antonio Barrera and Juan Manuel Marquez _ all the best fighters of the lower weight classes over which he has loomed for years.

"It's hard to fight with David, because this guy is not like Barrera or Morales (with a famous) name," Pacquiao said. "But I have to win this fight. I had to get in shape and get ready to fight, and I did it."

The extra weight might be Roach's biggest concern heading into the fight, but the veteran trainer claims Pacquiao has worked diligently to maintain the speed that's been unmatchable for nearly all of his opponents.

Diaz is confident he can match Pacquiao's tactics in a meetings of two left-handed fighters. Pacquiao sometimes strays from Roach's meticulous game plans, and Diaz has specialized in punishing fighters who make mistakes.

"I guess I've got to be the valedictorian for this fight," Diaz said. "I don't know if that's going to happen. He's going to do something, I'm going to do something, and we've both got to adapt."

Pacquiao dedicated the fight to the Philippines after a typhoon hit his nation last Saturday, possibly killing thousands. Diaz, the youngest son of Mexican immigrants, has been hesitant to invoke national pride, knowing Pacquiao's long history of beating Mexico's best.

"I want to give this fight to Mexico," Diaz said. "I know Manny doesn't like it, but he's been beating up on a lot of my countrymen."