LAS VEGAS (AFP) - Floyd Mayweather dethroned WBC welterweight champion Victor Ortiz with a controversial blind-side punch in the fourth round of their lively title fight on Saturday in Las Vegas. Mayweather knocked out Ortiz at 2:59 of the fourth as he hit the champion and fellow American after a break in the fight with a left-right combination while Ortiz had his hands down in the centre of the ring. It is protect yourself at all times. We touched gloves and that is all she wrote, the still-unbeaten Mayweather said. He did something dirty but we are not here to complain about what he did dirty or I did dirty. Referee Joe Cortez had stopped the fight in mid-round to deduct a point from Ortiz for head-butting Mayweather in the corner during a vicious exchange of punches. Ortiz had just finished apologizing twice to Mayweather for the head butt when Mayweather surprised him with a short left. After the fight, Ortiz and his corner complained about the way the referee handled the final moments of the fight, but Ortiz also took some of the blame for not protecting himself. It was called a break and I did as I was told, Ortiz said. I looked at the ref and then boom I was out. There was a little miscommunication by the ref. But I have no one to blame but myself. It was a learning experience.