Juan Manuel Marquez needed about three rounds to get comfortable as a lightweight. After that, he was nothing but bad news for Joel Casamayor.

Marquez won his 135-pound debut Saturday night, stopping linear champion Casamayor for the first time in the Cuban's career with a dynamic flurry late in the 11th round.

Marquez (49-4-1, 36 KOs) held title belts in two lighter divisions over the last five years, but moved up to lightweight in hopes of landing a third bout with Manny Pacquiao after going 0-1-1 against the pound-for-pound king.

The Mexican veteran proved those extra five pounds are nothing but punching power in a comprehensive win over Casamayor (36-4-1), the 37-year-old Cuban Olympic champion and defector who has unofficially ruled a talent-stacked division since beating Diego Corrales two years ago.

Marquez might be heavier now, but he's still light enough to leap onto the ropes to celebrate another big win.

"I figured this would be a tough fight until the end, but I was a more intelligent fighter," Marquez said. "I was watching out for myself, and I knew how to neutralize his left hand. I threw all my combinations, because I knew I couldn't win with just my right hand."

Marquez was tentative in the first three rounds, allowing Casamayor to take charge. When Marquez finally got aggressive, Casamayor wasn't able to keep up.

Marquez left nothing to the scorecards in the final minute of the 11th when he floored Casamayor with a right hand that spun the Cuban's chin. Marquez then showed impeccable finishing skills, landing several big blows before a glassy-eyed Casamayor went down for good on consecutive right hands with about 7 seconds left.

"I fought as a champion, but Marquez was the best this night," Casamayor said. "I deserve a rematch. Marquez knew how to control my punches. I had a bad night. I'm very emotional right now, but I honestly need the rematch."

Marquez probably has bigger goals to chase. He's among boxing's top talents, but the 34-year-old is running out of time to join the sport's elite stars _ and he was surpassed in the hearts of many Mexican fans by welterweight Antonio Margarito, who stopped Miguel Cotto in July to become the boxing-mad nation's highest-profile champion.

This TKO should be a big step in getting Marquez back to the top, particularly if a certain Filipino phenomenon happened to be watching. Pacquiao, who made his own lightweight debut in June, is expected to move back to 135 pounds after his big-money welterweight bout against Oscar De La Hoya, Marquez's promoter.

"We moved up in weight, and we will fight anyone that our promoter wants," Marquez said. "He was the best lightweight in the world, and he has strong counterpunches."

Casamayor holds none of the major title belts, but has beaten both the late Corrales and Nate Campbell, who holds the other three 135-pound title belts after upsetting Juan Diaz last March. Casamayor appeared to be on his career's downslope in recent fights, winning a questionable decision over Jose Armando Santa Cruz and struggling in a win over Michael Katsidis last spring.

He still presented all kinds of awkwardness for Marquez. Few fighters have ever looked good against Casamayor's array of head butts, elbow blows and general left-handedness _ but Marquez managed to shine.

The punch stats were fairly even, with Marquez landing higher percentages in total punches and power punches to counter Casamayor's higher overall total. The fight was tight on the judges' scorecards, with two judges seeing the fight even after 10 rounds, while Glenn Feldman favored Marquez 97-93.

Marquez began with extreme caution, showing none of the cavalier showmanship of his two lively fights with Pacquiao. Casamayor was happy to pick away with left-handed shots while controlling the first three rounds.

But Marquez opened a cut above Casamayor's right eye in the fourth round, apparently from an accidental clash of heads. Marquez turned the physical tide with a persistent jab and a higher work rate, limiting Casamayor to mostly single punches that did no damage.

Mexican fans dominated the MGM Grand crowd, booing Casamayor heartily _ but Casamayor has loved being the villain since winning his gold medal at the Barcelona Games 16 years ago. The heavily bearded Cuban entered the ring in a Mexican sombrero and pitch-black trunks.

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