Joel Casamayor (left) beat Diego Corrales by split decision

America's Corrales had already been stripped of the title when he failed to make the weight on Friday.

But the fight went ahead with the agreement Casamayor would claim the belt if he won.

"I was worried when the fight went to the scorecards," said Cuba's Casamayor. I'm thankful the judges did the right thing."

Both fighters were cautious in the opening two rounds but Casamayor started to press the action in the third, jarring Corrales with lefts to the jaw.

At the end of the fifth Casamayor went down from a slapping left hook to the side of the head and received a standing count from referee Kenny Bayless.

I thought I won -I had him hurt in the ninth round Diego Corrales

"I slipped," said Casamayor. "It was not a knockdown. I was pushed."

The Cuban came out strongly at the start of the sixth but as the fight went on both men had strong moments, Casamayor winning the eighth and Corrales landing a series of hooks and heavy right hands to take the ninth.

Casamayor appeared to wobble in the 10th after Corrales landed a left hook high on the temple, but the Cuban recovered well.

"I thought I won," said a disappointed Corrales. "I had him hurt in the ninth round."

Saturday's bout was the third meeting between the two. Casamayor won the first in October 2004 by TKO and Corrales took the rematch five months later by split decision.

With the victory Casamayor's record improves to 34-3-1 with 21 knockouts, while Corrales falls to 40-4 with 33 KOs.

Needing to make the official 135-pound (61.3kg) limit, Corrales was never closer than four pounds, reports said.

The bout was stopped in the sixth round when Donaire suffered a jaw injury from an accidental head butt.