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 Saturday night, 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 keep up.

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 punishment 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. After finally flooring Diaz, Pacquiao tugged on Diaz's arm in support before leaping onto the ropes in celebration.