Thanongsak Simsri (40-1, 35 KOs) charged out of the blocks with excellent body work and wasted no time in his first title defense, scoring a second-round knockout win over Sergio Mendoza (27-1, 23 KOs) at Japan's famed Korakuen Hall on Monday.

Heading back to the same country he won the belt last June after a hard-fought split decision win over Cristian Araneta, Simsri didn't box like an underdog and delivered a vicious finish to retain the IBF junior flyweight belt.

Mendoza boasted the physical advantages but didn't know what hit him.

While the Mexican southpaw caught the champion's attention with a hook in round two, the 26-year-old wasn't allowed to settle by Thailand's only current beltholder in a discipline where Southeast Asian hopefuls are often not given the respect their endeavors warrant. Performances like this quick-fire knockout help spotlight the opposite.

Simsri commanded proceedings behind his excellent southpaw jab and a pair of right hands wobbled Mendoza backwards midway through the second frame, foreshadowing a furious finish. A five-punch flurry, punctuated by a left hook crumbled the challenger against the ropes and he looked shellshocked, though more was coming.

A right hand sent him crashing down once more as he shaped to throw a counter and mercifully, referee Koji Tanaka waved it off.