All five of Cotto's title defences have been knockouts

Cotto's fifth defence and 22nd knockout in 26 unbeaten fights finished in the eighth round when the Italian challenger was unable to continue.

"He did not hurt me. He had his good punches but this was our night," said Cotto, 25. "It wasn't an easy fight."

America's Paul Malignaggi (21-0, 5 KOs) will be his next opponent on 10 June at New York's Madison Square Garden.

Branco's left eye started to swell in the first round, and Cotto quickly went to work on the challenger's right eye in the second round as well.

By the end of the fight, Branco's right eye and the right side of his jaw were puffed and slightly bleeding.

Branco, who punched Cotto below the belt in the fourth round, complained several times to no avail about low blows and headbutts.

Malignaggi watched the fight and was impressed by the champion.

"Cotto showed today he was the best fighter, but Branco didn't show much besides a flicking jab," he said.