In 2007, he won a Thai national title in the Light Flyweight division, and was released from prison for good behaviour the following day having served one year.

In his first defense, he traveled to Japan and earned a split decision over undefeated two-division champion Kazuto Ioka, who was making his flyweight debut.

On March 7, 2015, he earned a unanimous decision over undefeated two-time Olympic gold medalist Zou Shiming.

Ruenroeng (16-0, 5 knockouts) was credited with two knockdowns against Casimero (21-3, 13 KOs), beginning with a counter right in Round 2 that caught the 25-year-old from Ormoc City lunging in.

Casimero appeared to knock Ruenroeng down in Round 3 when a counter left hook caused his glove to touch the canvas, but referee Larry Doggett ruled it a slip.

Amnat was doing his job as a boxer how to win.” The roughhouse tactics detracted from an otherwise crafty, resourceful performance from the Thai incumbent champion, whose jab disrupted the rhythm of Casimero, who held the IBF junior flyweight title for two years before being stripped last year for failing to make weight for his fight with Mauricio Fuentes.

Ruenroeng, 35, has now defended his belt four times successfully since winning it in January 2014 with a victory over Filipino contender Rocky Fuentes.

He won his opening bout before losing in the round of 16 against Sofiane Oumiha, a younger fighter representing France.