Simsri blasted Mendoza into a career-first defeat in two rounds at the famed Korakuen Hall in Tokyo, Japan on April 13. Although a slight underdog pre-fight, he was determined to make the first defense of his world title.

"This fight is one where I can't underestimate anyone for even a split second because I know Mendoza is a great fighter from Mexico," Simsri (40-1, 35 KOs) told The Ring.

Simsri, The Ring’s No. 3 ranked junior flyweight, had the fight's first big moment and heavily dropped Mendoza (27-1, 23 KOs).

"It was a left hook that landed squarely on a vital spot, and that made me confident I can finish the fight," he said.

"But Mendoza is definitely a very determined Mexican boxer. He got back up and continued fighting, making me realize I needed to finish the fight as quickly as possible before he could react."

Which is exactly what Simsri did scoring a second and decisive knockdown, which prompted referee Koji Tanaka to call a halt at 2:32 of the second round.

While the Thai showed no empathy inside the ring, he did afterwards towards his rival.

"After the fight, I was worried about Mendoza, but we couldn't meet again and that's what I regret."

There was no big celebration for the former farmer turned world champion, who kept things low key.

"After leaving the boxing ring, my trainer and I went out for a normal meal; there was no special celebration," he said.

Simsri and his manager-trainer Poom Kosonset will head to Osaka and then travel home on April 20, before turning their attention to what is next.

"I definitely want to fight in a big one," he said. "I want a unification. My team and I will discuss it further before making a decision on the next fight."