Paul Butler has failed in his bid to become undisputed world bantamweight champion after being stopped in the 11th round by Naoya Inoue.

As far as undisputed fights go, Butler was one of the biggest outsiders in boxing history, partly a consequence in facing one of the sport's pound-for-pound stars and biggest punchers.

The expectant Koto-Ku crowd were anticipating another early highlight-reel knockout as Inoue bid to earn further recognition at the top of the sport.

However, Butler appeared to be in survival mode from the early rounds, negating some of what Inoue had to offer and lower the atmosphere in the crowd.

While few could criticise Butler's tactics given the gulf in class, it made for a poor spectacle, and Inoue became increasingly frustrated despite comfortably winning every round of a one-sided contest.

Nevertheless, in the penultimate round, Inoue got the 21st stoppage of his 24-fight career, a body shot starting the process of pummelling Butler against the ropes before he hit the canvas.

Despite just seconds remaining in the round, Butler never looked like getting to his feet, losing the WBO belt which he earned having previously won an interim world title fight in April.

After securing all four belts at 118lbs, Inoue confirmed that he will now step up to super-bantamweight in a bid to become a four-weight world champion.

There are currently two belt holders in that division, and Inoue is eligible to face WBO and WBC champion Stephen Fulton as per the former's regulations.

However, Inoue may choose to take a separate fight to acclimatise to the step up in weight, aware that his star power in the lower weights will inevitably lead to an eventual world title shot in 2023.