Naoya Inoue was described "scary" and "unstoppable" as he claimed the IBF world bantamweight title from Emmanuel Rodriguez in a stunning stoppage win.
The Japanese fighter, 26, floored Puerto Rico's previously unbeaten Rodriguez three times in round two, when the bout was waved off.
Known as 'The Monster', Inoue now has 16 knockout wins from 18 outings.
British trainer Dave Coldwell said it was "special" to see a fighter show such power at the sport's top level.
WBC world flyweight champion Charlie Edwards tweeted: "Wow Inoue is one scary, scary man, what a monster!"
Inoue has now beaten men who have been world champions in his last three fights, which have lasted less than eight minutes in total.
British fighter Gavin McDonnell, whose brother Jamie was one of the three beaten men, tweeted: "Inoue is some fighter beating three world champions in four rounds is crazy. Inoue is unstoppable for me.
"Name another champion who's cleaning up like him in the fashion he does? Our lower weights get no credit."
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Former British light-heavyweight champion Frank Buglioni tweeted: "Inoue true to his name is a legitimate monster."
Ex-British middleweight champion Matthew Macklin said: "Inoue is a beast. The hardest puncher pound-for-pound in boxing."
And British heavyweight Dave Allen tweeted: "I'm fully on the Inoue train unbelievable. He's nearly 10 stone lighter than me but I wouldn't fancy a crack off him. I think if he hit anyone flush no matter how big you are you're going over."
Rodriguez, 26, who was left bloodied and fell to a crushing left hook, a body shot and lastly a flurry, had caught the eye with several impressive displays in his 19 previous outings.
But Inoue took his world title and a place in the final of the World Boxing Super Series bantamweight tournament where he will face Filipino fighter Nonito Donaire, who holds the WBA belt, meaning the victor will unify the titles at 118lbs.