Thai champion Pongsaklek Singwangcha stopped Japanese challenger Hayato Asai with a fifth-round technical knockout Sunday to retain the World Boxing Council (WBC) flyweight title.

In his first title defense, Pongsaklek brutalized the seventh-ranked Asai with stinging punches from the early stages of the bout at Aichi Budokan as he overwhelmed the challenger with greater power and speed that led to two knockdowns in the fourth round.

After flooring Asai with powerful right-hooks, Pongsaklek punished him again in the fifth with a rampaging onslaught that prompted the referee to stop the fight after 47 seconds.

"I felt like I could go for a knockout in the second round. The match went exactly as I expected. Asai's punches were somewhat strong but frankly they were no big deal. I want to defend the title as long as my body holds up," Pongsaklek said.

"I realized for the first time that I was here after hearing the national anthem. But I just couldn't get my feet moving and I still have a long way to go in boxing," Asai said.

Pongsaklek left the fight with 41 wins, including 24 knockouts, and two losses, while Asai is 16-3-2, including 12 knockouts.