Teofimo Lopez beat Vasyl Lomachenko by a unanimous points decision in Las Vegas to become the undisputed world lightweight champion.
The American’s win over the Ukrainian means he now adds the WBA, WBO and WBC ‘Franchise’ titles to his IBF belt.
Lopez, 23, dominated the first half of the fight and, despite a late rally by Lomachenko, was awarded a 116-112, 119-109, 117-111 win by the judges.
“I am ready to take over the world,” Lopez said.
The result means he is the youngest fighter to become a four-belt undisputed champion and he maintains his unbeaten record with 16 wins from 16 bouts.
The fight between the two rivals had been eagerly awaited but took place without any fans because of the coronavirus pandemic.
Lomachenko, 32, was kept quiet early on and, although he put in a strong effort in the later rounds, it was not enough to stop him suffering a second defeat from his 15 fights.
“I think I won the fight,” Lomachenko said after his first loss in six years. “But I am not going to argue it now.
“In the first half of the fight he won more rounds. In the second half I took it over. I don’t agree with the scorecards.”
Mike Costello, BBC 5 Live boxing correspondent
Boxing has a new star and the story of Teofimo Lopez might only be starting, in terms of wider appreciation.
For two years, his father and trainer Teofimo Sr has been predicting what we saw last night. Forget the narrative of ‘Loma the boxer against Lopez the puncher’, he would insist, one of the all-time greats of the sport would be out-thought and out-fought. And so it was.
The contention that Lomachenko started too slowly and conceded the early rounds too readily is a slight on Lopez. In a low-scoring first half of the fight - and against a fleet-footed opponent - Lopez used single jabs and stiff right hands to the body to gain control, waiting patiently for opportunities in building a lead on the scorecards. Lomachenko was forced to increase his work rate in the second half and Lopez showed impressive maturity, at 23, in managing a potentially turbulent spell.
I scored it 116-112 (eight rounds to four) in favour of Lopez and it’s the mark of a special fighter that when the momentum appeared to be swaying against him late on, Lopez responded by producing a glorious final round.
All in all, a performance to match Tyson Fury’s against Deontay Wilder as the best of the boxing year so far.