Cotto (left) was on top for most of the fight

Judah never really recovered from a cut to the right eye and two low blows early on at Madison Square Garden.

Cotto, who was cut inside the mouth and had blood running down his chest, took charge after the third round and had Judah down on one knee in the ninth.

Two rounds later Cotto floored Judah with a left hook. He got up but the fight was stopped moments later.

Cotto was penalised a point in the third round for his second low blow while the other came in the first.

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After defending his title for a second time, the Puerto Rican's record improved to 30-0 with 25 knockouts, while Judah fell to 34-5, also with 25 KOs.

"I expected a tough fight and that's exactly what I got," said Cotto afterwards.

"He sure did land some great punches, but I was prepared for them. I trained hard. I could tell, round by round, I was taking over the fight."

New Yorker Judah, the division's former undisputed champion, argued that the illegal blows played a role in his defeat.

"He hit me hard twice and the referee didn't do anything about it," he said. "I thought they were intentional. Those low blows took a lot out of me. I want a rematch."

The American (24-0, 16 KOs), who took the WBC crown from the previously unbeaten Tomasz Adamek in February, was making his first defence.

Dawson's next opponent could be Antonio Tarver who regained the IBO light heavyweight belt with a 12-round decision over ex-kickboxer Elvir Muriqi on the same card.