LAS VEGAS — Although Manny Pacquiao is the new 135-pound champion, he's no mere lightweight.

At any weight, in any ring, the Filipino phenomenon looks like the best pound-for-pound boxer in the world.

Packing five new pounds of power in his usual stunning hand speed, Pacquiao captured a title belt in his fourth weight class tonight, stopping David Diaz in the ninth round to claim the WBC lightweight championship at the Mandalay Bay Events Center.

After starting his career 13 years ago at 106 pounds, Pacquiao (47-3-2, 35 KOs) has evolved into a dominant fighter in five divisions. His lightweight debut was every bit as action-packed as his long history of brawls at lower weights — and like most of his opponents, Diaz (34-2-1) couldn't match Pac-Man's ferocious pace.

"I feel much, much stronger and more powerful at 135," said Pacquiao, the first Asian boxer to win titles at four weights. "This is where I plan to stay. I did real well. I was really surprised it wasn't stopped sooner."

Three months ago, Juan Manuel Marquez stretched Pacquiao to the limit before losing a split decision in the same ring in perhaps the year's best bout so far. Pacquiao took much less punishment this time, but Diaz was remarkably tenacious in the face of nonstop attacks — until Pacquiao sneaked home a left hand that dropped Diaz's bloody face to the canvas.

Diaz, the likable but unlikely champion from Chicago, knew he faced long odds — 4-to-1 at fight time — in his second title defense. The former U.S. Olympian hung in despite severe cuts and weary legs that wobbled with each of Pacquiao's big punches.

Pacquiao was relentless with his right hook, apparently capitalizing on something seen by trainer Freddie Roach in Diaz's defense.

"His punches are just too fast," Diaz told his corner after the sixth round.

Diaz's face was dripping blood by then, and both fighters' white trunks were shaded pink by the eighth, when Pacquiao battered Diaz relentlessly. Referee Vic Drakulich stopped the bout before even counting to 10, and Pacquiao tugged on Diaz's arm in support before leaping onto the ropes in celebration.

"It was his speed," Diaz said. "It was all his speed. I could see the punches perfectly, but he was just too fast. He boxed me more than I thought he was going to box. I said to Freddie (Roach), 'It's the best I've ever seen him box.' Freddie said, 'Me too. That was our game plan.'"

Pacquiao threw 788 punches to Diaz's 463, also landing 10 percent more of his blows. Pacquiao also jabbed well with remarkable discipline for an instinctual brawler, but Diaz was hurt most by Pacquiao's 180 power shots that connected.

Pacquiao started fighting as a scrawny 16-year-old in the Philippines, but he grew into a dynamic competitor who won world titles at 112, 122 and 130 pounds. He also knocked out linear champion Marco Antonio Barrera at 126 pounds in November 2003, giving Pacquiao major victories at every weight class he has entered.

His move to 135 pounds, while seemingly inevitable after Pacquiao largely cleared out the junior lightweight division, led some to worry whether the extra bulk would compromise Pacquiao's famed speed. Even Roach acknowledged his fighter might not be quite as fast.

Nobody is worried any more — least of all Roach.

"That was beautiful," Roach said. "The game plan was not to stand and trade, because Diaz is too dangerous. The plan was to go in and out, outbox him, do what Manny does best. He did everything that we asked him to do."

Some thought Pacquiao's next move could be to bulk up even further, perhaps for a wildly lucrative fight with England's most popular plugger, Ricky Hatton. Pacquiao seems more likely to stick around to fight other lightweights, including a possible bout against Humberto Soto, who lost a curious disqualification Saturday in an undercard bout.

"I can fight in November," Pacquiao said. "Who I fight is the job of my promoter (Bob Arum)."

Pacquiao has made his career on a series of exciting brawls with the best Mexican fighters of the post-Julio Cesar Chavez era, going 5-1-1 against Barrera, Erik Morales and Marquez, who lost a supermodel-thin split decision to Pacquiao last March.

Meanwhile, Diaz has made a career out of defying meager expectations, starting with two surprising victories over Zab Judah for a spot on the 1996 U.S. Olympic team. After quitting the sport for nearly two years early in this decade, Diaz earned his title nearly two years ago in a stunning 10th-round knockout of Jose Armando Santa Cruz.

The unlikely victory was the height of success for Diaz, the youngest of nine children born in Chicago to Mexican immigrants. He became a mid-major sports celebrity in Chicago, throwing out a first pitch for his beloved Chicago Cubs and earning the admiration of Blackhawks coach Denis Savard, who was scheduled to accompany Diaz into the ring Saturday night.

Mandalay Bay was filled largely with Filipino fans, including an overly optimistic man whose sign read, "Pac-Man, Marry Me!"