Japan's Naoya Inoue became an undisputed world champion at a second weight on Tuesday after knocking out the Philippines' Marlon Tapales in the 10th round to claim all four super-bantamweight belts.
The unbeaten Inoue, nicknamed "Monster", sent Tapales to the canvas with a huge right hand in Tokyo to add the WBA and IBF titles to his own WBC and WBO belts.
Inoue, who took his record to 26-0 with 23 KOs, becomes only the second man to unify all four world titles in two different weight classes.
American Terence Crawford became the first after beating compatriot Errol Spence for all the welterweight belts in July.
"I think super-bantamweight is the most suitable weight class for me at the moment," said the 30-year-old Inoue.
"Next year and the year after that, I want to prove that I can become an even stronger fighter."
Inoue completed his rampage through the bantamweight division in December last year, becoming the first undisputed world champion at the weight in half a century before vacating his titles.
He needed just two fights to become the super-bantamweight division's first-ever undisputed champion.
He beat American Stephen Fulton in July in his debut at the weight to claim the WBC and WBO belts.
But he had to dig deep to beat Tapales, who clawed his way back into the fight after Inoue floored him in the fourth round.
"He was very tough with a strong mentality," said Inoue.
"I think the way I was able to knock out a strong fighter like that in the 10th round is proof of all I've been doing, so I'm relieved."
Inoue went on the attack straight away against Tapales, who upset Uzbekistan's Murodjon Akhmadaliev by split decision in April to win the IBF and WBA titles.
Inoue landed some early punches while the 31-year-old Tapales stayed in his defensive shell.
The Japanese fighter dropped his opponent at the end of the fourth round after a flurry of head shots, only for Tapales to get up and beat the count.
Inoue went straight back to work at the start of the fifth, although Tapales also landed some big shots.
Tapales steadied the ship but Inoue maintained the upper hand and finished his opponent with a ferocious straight right hand.
"He kept a poker face throughout and didn't show that my punches were doing him any damage, so I was quite surprised when he went down in the tenth round," said Inoue.
Tapales saw his record drop to 37-4 with 19 KOs.
Inoue has won world titles in four different weight divisions, having also triumphed at the light-flyweight and super-flyweight levels.
He knocked out England's Paul Butler in December last year to become the first undisputed bantamweight world champion since Panama's Enrique Pinder in 1972.
He also became only the ninth undisputed world champion since the four-belt era began in 2004, and the first in the bantamweight division.
After vacating his titles, his younger brother Takuma claimed the WBA bantamweight belt in April with a win over Venezuela's Liborio Solis.