It was shaping up as an action classic, but a Junto Nakatani left hand shattered Angel Acosta's nose in the bout's opening stages, and that spelled the beginning of the end for Acosta.

Before a sold out crowd of 4,545 at Casino Del Sol in Arizona, Nakatani defended his WBO flyweight world title with a fourth-round stoppage after referee Rocky Burke and the ringside physicians halted the fight due to the damage Acosta sustained.

Nakatani (22-0, 17 KOs), from Japan, won the vacant world title last year and made a splash in his United States debut. Acosta (22-3, 21 KOs), from Puerto Rico, previously held a world title at light flyweight and saw his two-bout winning streak come to an end.

Now the Japanese fighters want to face the other champions in his weight class - like (IBF) Sunny Edwards, (WBC) Julio Cesar Martinez and (WBA) Artem Dalakian.

Nakatani said, “I caught him in the first round right in the nose and I was able to use my pace to fight him, so that worked out really well. I knew (I had broken his nose). I thought it was a good win. I want to unify the titles.”

Acosta will have to go back to the drawing board. He explained after the fight that he wanted to continue with the contest, but admitted to having breathing problems from the start of the second round, as blood was flowing down his throat.