Antonio Margarito celebrates his 11th-round TKO victory over Miguel Cotto on Saturday. (Ethan Miller/Getty Images))

So that's why every welterweight in the world was so scared of Antonio Margarito.

Margarito stopped Miguel Cotto in the 11th round Saturday night in Las Vegas, blemishing Cotto's unbeaten record and claiming the WBA 147-pound title with one last incredible barrage of punches.

Margarito (37-5, 27 KOs), the Mexican star so often ducked by the division's best fighters in recent years, dropped the Puerto Rican champion twice in the 11th after several rounds of relentless pressure in a fight that lived up to its lofty billing at the MGM Grand Garden.

"I told my corner I would wear him down and then knock him out," said Margarito, who won his third welterweight belt. "He never hurt me, but that was the game plan, to come out early strong and to wear him down and knock him out. I got him with body shots, and then I hit him in the head, and then I knocked him out."

Cotto (32-1), the respected champion attempting his fifth title defence, won the early rounds with defence and timely counterpunching. Margarito took several major shots on his tough chin, yet still kept up the same relentless attack that finally paid off in the middle rounds.

With Cotto bleeding and woozy, the champion's corner stopped the fight with 55 seconds left, sending Margarito's team into a delirious celebration of a long-awaited victory. Cotto, unable to speak clearly through tears and welts, was taken to a hospital from his locker room.

"I am very proud and very happy I was able to give the fans a great fight," Cotto said. "Life continues. It's not over for me. I'm going to take a long rest, decide what to do next. This night was Margarito's night. He's an excellent fighter. He did his job better than I did."

From the opening round, the fight matched every expectation in the Mexico-Puerto Rico rivalry that has produced innumerable memorable fights in the last three decades. Their countrymen filled the arena with cheers, flags and chants, and Margarito said he drew strength from the support — although his motivation already was several years in the making.

Margarito has long been a looming nightmare for the division's top fighters because of his heedless style and tough chin. Floyd Mayweather Jr. turned down an $8-million US payday to avoid facing the "Tijuana Tornado" in 2006 — a dodge that resonated with Cotto, who also couldn't get the Pretty Boy to return his promoters' calls.

This fight came together in April when Cotto and Margarito trounced two challengers on the same card in Atlantic City. Promoter Bob Arum immediately gave both fighters the matchup they craved, putting his two top welterweights together for a joint debut as Vegas headliners — though Cotto made $3 million to Margarito's $1.5 million.

With this career-making win, Margarito will be among the finalists for the wildly lucrative spot opposite Oscar De La Hoya on Dec. 6 in the Golden Boy's farewell fight in the same MGM Grand ring. De La Hoya previously was circling Margarito for the fight, but Cotto's battered face might give De La Hoya second thoughts about both fighters.

"Oscar De La Hoya is one of the best," Margarito said. "If he comes through with his promise, we can give Mexicans a true battle."

If De La Hoya goes with Cotto, Manny Pacquiao or a lesser challenge, Margarito could be looking forward to a unification fight with the winner of next weekend's IBF title fight between Zab Judah and Joshua Clottey.

The loss clearly stunned Cotto, who had shown remarkable resourcefulness after being staggered in two 140-pound fights earlier in his career. Though Cotto carried the early action, Margarito bloodied Cotto's nose and mouth before picking at the wounds throughout the middle rounds.

Cotto landed 43 per cent of his 655 punches, but Margarito's superior work rate was reflected in his 987 total punches. Margarito jabbed poorly, but landed 237 power shots to Cotto's 179 — most in the final few rounds.

Margarito, who took three of his five career losses as a teenager in Mexico, lost his WBO welterweight title to Paul Williams last year with an uncharacteristically slow start. He claimed the IBF title three months ago by battering Kermit Cintron, but had to give up that belt to make the match with Cotto — a gamble that paid off immensely.

Cotto appeared confident from the opening bell, slipping his jab through the small gap in Margarito's defence almost from their opening collision. The expected brawl began in earnest in the second round, with both fighters landing heavy shots to the head.

Cotto seemed superior until Margarito's work paid off in the seventh, when he stunned and bloodied Cotto with a flurry capped by a left hook. Margarito chased him for the rest of a punishing round, reducing Cotto's once-confident swagger to a stumble.

Cotto rallied in the 10th, but Margarito still was relentless.

Cotto began spitting blood, and another barrage from Margarito dropped him to one knee 80 seconds into the 11th. Cotto was wobbly, and Margarito chased him until the Puerto Rican star finally went down again. Margarito was ahead on two of the three judges' scorecards at the time.