Mandalay Bay, Las Vegas - Two-time Olympic gold medalist Guillermo Rigondeaux retained his super batamweight title on a first-round knockout over Moises Flores when he landed a punch after the bell.

Rigondeaux and Flores were trading punches when the bell rang to end the first round and both threw after the bell. Rigondeaux's punch landed, and Flores dropped to the canvas where he was counted out.

Nevada boxing officials huddled for several minutes and watched the replay before ruling the punch was legal.

Rigondeaux, who won his gold medals for his native Cuba, improved to 18-0 with 12 knockouts as a pro, while Flores, from Mexico, fell to 25-1.

"The Mexican was a brave kid," said Rigondeaux.

"I commend him for getting in the ring with me. He has more guts than a lot of these other guys. We both threw combinations at the same time at the end of the first round. But mine was quicker and more accurate. It was only a matter of time. I fight to give the best performance to the public and all the fans. I am making everyone disappear at 122. I am always available. Tell me who is next. I want all of them, and will take them out one by one. I hope the whole world sees what it is like to get in the ring with me. I am tired of the press and everyone saying I am boring. You see what happens when someone brings the fight to me."

Flores, who believed the punch was after the bell replied, "It's not fair. It's clear that the bell rang. He didn't throw a punch the whole round. I was winning the round and he waited for after the bell to throw punch when I dropped my hands down."