Devin Haney claimed a unanimous points victory over Regis Prograis to secure the WBC light-welterweight title in San Francisco.
American Haney dominated his compatriot and knocked him down in the third round, with all three judges scoring the bout 120-107 in Haney’s favour.
It was his first fight at 140 pounds, having previously been the undisputed lightweight champion.
“I felt so much stronger – 140 got a new king,” Haney, 25, said.
He vacated his 135lb WBC, WBA, IBF, and WBO belts in November to move up a weight class.
He now holds a 31-0 record, including 15 knockouts, while the loss was Prograis’ first since October 2019.
On the undercard, Australian Ebanie Bridges suffered a shock defeat by Miyo Yoshida to lose her IBF bantamweight title.
Japan’s Yoshida was a massive underdog, coming into the contest with just 20 days’ notice and off the back of a loss in her previous fight.
But Yoshida, previously a world champion at super-flyweight, controlled the bout through the 10 rounds and was able to evade Bridges’ efforts to produce a last-ditch knockout.
Yoshida, 35, burst into tears as the scorecards were read out, 99-91, 99-91, and 97-93, with her young daughter Mina celebrating at ringside.
With her victory, Yoshida improved her record to 17 wins and four losses, while Bridges slumped to her first defeat since April 2021.
