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 Haney’s 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.
Haney 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 victory, Yoshida improved her record to 17 wins and four losses, while Bridges slumped to her first defeat since April 2021.