OSAKA (AFP) - Japan's Koki Kameda knocked out Mexican challenger Mario Macias in the fourth round to defend his World Boxing Association bantamweight title on Wednesday. The knockout came two minutes four seconds into the stanza when Kameda fired four punches to the stomach to send Macias onto the floor for the third time in the bout. "I feel I was able to hit powerful punches. I'm in good form today. It's because this is my home town," said Kameda , who floored Macias with a left hook in the first and third rounds. "I think this was the best fight I fought in the bantam class. Now I'm going to support my brother, who will challenge the WBA super flyweight champion Tepparith Kokietgym of Thailand." It was Kameda 's third defence since winning the vacant title when he beat Alexander Munoz of Venezuela in December last year, stretching his record to 27 wins, including 17 KOs, against one defeat. Kameda is the eldest of a trio of boxing brothers who have bad-boy images in the media and among boxing fans. Second brother Daiki was suspended from boxing for a year after his failed title bid against then World Boxing Commission flyweight champion Daisuke Naito in October 2007 for using dirty tactics including wrestling the veteran champion to the canvas. Koki Kameda was reprimanded by the Japan Boxing Commission for urging his brother to fight dirty. Their father, Shiro Kameda , has been barred by the WBC from serving as a cornerman in its matches for abusing match officials and has been slapped with a life ban by Japan's boxing authority. Macias, 26 and ranked 12th the WBA , saw his record reduced to 23 wins, including 11 KOs, against eight defeats and one null and void.