Juan Manuel Marquez and Juan Diaz both say they've reached a pivotal moment in their boxing careers.

Two of the world's top lightweights will battle for Diaz's IBO championship and the vacant WBA and WBO titles on Saturday night at the Toyota Center.

Marquez (49-4-1, 36 KOs) is a former featherweight and super featherweight champion fighting for only the second time at 135 pounds. He beat Joel Casamayor by technical knockout last September in his lightweight debut and needs a victory over Diaz to have a chance of lining up another bout with nemesis Manny Pacquiao. The two fought to a draw in May 2004 and Pacquiao won a controversial decision in the rematch last March.

But first comes Diaz.

"If I win," Marquez said, "it could mean great things for me, even more important fights."

The Houston-born Diaz (34-1, 17 KOs) is trying to win back the WBA and WBO belts he lost to Nate Campbell last March. Campbell was stripped of the titles earlier this month when he came in overweight for his fight with Ali Funeka.

"This is the type of fight I've been waiting for my whole life," Diaz said. "They're going to have to carry me out with a stretcher in order for me to lose that fight on Saturday night."

The 35-year-old Marquez is a national hero in Mexico, but he agreed to fight Diaz in his hometown. He's also 10 years older than Diaz and admits that Diaz is a high-volume puncher who brings an awkward style.

But Marquez just smiles when reminded of Diaz's apparent advantages.

"I feel very confident because I have been training very hard," Marquez said. "I know I have a difficult fight, but not impossible to win."

Diaz rebounded from his loss to Campbell by beating Mick Katsidis in Houston last September. Marquez is a steep upgrade in class, a 15-year professional known for accurate punches and knockout power.

Diaz said his plan is to wear down Marquez and pounce in the late rounds.

"He's a great, legendary fighter," Diaz said. "He's very smart in there, but he's also 35 years old. I'm 25. I believe my youth is going to carry me to the victory."

Marquez was 134 1/4 pounds and Diaz was 134 1/2 at Friday's weigh-in.

Before they face off on Saturday night, unbeaten WBA featherweight champion Chris John will make his North American debut against Houston native Rocky Juarez, a silver medalist at the 2000 Olympic Games.

John (42-0-1, 22 KOs) has boxed mostly in his native Indonesia. He wants to put on a show for the national-television audience on Saturday with the hope of landing more fights _ and bigger paychecks _ in America.

"It's the most important fight of his life," said Craig Christian, John's trainer. "If he loses here, they won't want him back. He wants to fight here all the time. He wants to put on his best performance for the American public so, hopefully, they'll want him back."

John won the belt with a 12-round decision over Osamu Sato in Japan in June 2004. He settled for a technical draw against Jose Rojas in December 2004 and has won eight title defenses since, including a 12-round decision over Hiroyuki Enoki in Japan last October.

Christian expects Juarez to come straight at John and try to corner him. Christian said John is the more versatile fighter and will be able to adjust to whatever strategy Juarez throws at him.

"If Rocky wants to fight, Chris will fight. If Rocky wants to box, Chris will box," Christian said. "We're ready for anything."

Juarez (28-4, 20 KOs) is 0-4 in professional world-championship bouts. He'll turn 29 in April and feels an urgency to break through on Saturday.

"Any opportunities for a title, you have to take them. How many more chances can I get?" he said. "This fight, I'm just ready, ready to fight and win. I just have to go out and do what I know I can do."

John and Juarez both weighed in at just over 125 pounds on Friday.

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