Thanongsak Simsri vs. Sergio Mendoza - April 13, 2026

[Ruthless-RKO]

Thanongsak Simsri primed for title defense against 'dangerous' Mendoza

Thanongsak Simsri will put his IBF junior flyweight title on the line for the first time when facing mandatory challenger Sergio Mendoza on April 13.

Simsri, The Ring's No. 3-rated junior flyweight, is well versed on what to expect from his tough Mexican opponent but believes he'll have more than enough to emerge victorious.

"In his 27 fights, he's undefeated," Simsri (39-1, 13 KOs) told The Ring. "He's definitely a great boxer, but I have no worries, because I always do my best in every fight. It might be a pretty dangerous match, but I have confidence in my experience, my team, and my preparation, because I never underestimate my opponent in any fight.

"Mendoza is a skilled boxer with powerful punches, but I believe I can stop him as well."

The two will meet on neutral turf at the famed Korakuen Hall in Tokyo, on a Ohashi Promotions show.

Simsri has fought overseas on several occasions. Mendoza will be fighting outside his homeland for the first time.

"That might be an advantage for me," he said. "I've competed in Japan a lot, and this is his first time competing abroad. But I won't underestimate him for a second."

The 25-year-old from Thailand hopes to put the division on notice with a win.

"Of course, I want to be champion in every organization," he said. "But I have to get through this fight first."

Simsri's manager Ookami Tora has known him for many years. He believes that now his fighter is a world champion, he won't give it up easily.

"We won't be complacent, and we definitely won't give up," the manager said.

"We never thought of ourselves as world champions, but we only thought that we are the real deal. We will never stop developing. There are so many talented people in the world, so we need to practice even harder."

Mendoza (27-0, 23 KOs), who is unranked by The Ring, has been a professional since 2018.

The 25-year-old southpaw from Hermosillo holds notable wins over Angel Ramos (KO 3), Joel Cordova (UD 10) and, most recently a third-round knockout of Mpumelelo Tshabalala in their IBF title eliminator on November 22.

[handsofstone]

Simsri KOs Mendoza in 2 rounds, Mendoza done ok in the 1st, tall southpaw but 2nd round Simsri was putting it on him, teeing him up with right hands before a right/left dropped Mendoza hard, he got up but Simsri poleaxed him with a right and that was all she wrote

[margaret thatcher]

seems like this simsri fellow is the best thai at the moment, the only one consistently winning regularly outside thailand

[Ruthless-RKO]

SIMSRI ON NEXT STEPS AFTER MENDOZA WIN: 'I DEFINITELY WANT A BIG ONE'

While the IBF junior flyweight title fight between Thanongsak Simsri and mandatory challenger Sergio Mendoza appeared evenly poised pre-fight, it proved anything but.

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."