Jessica McCaskill handed Cecilia Braekhus her first professional defeat in a huge upset to become the undisputed world welterweight champion.
American McCaskill, 35, won by majority decision in Tulsa to take Braekhus’ WBA, WBC, IBF, IBO and WBO belts.
Victory would have seen Norway’s Braekhus, 38, beat Joe Louis’ streak of 25 straight title defences in an 11-year reign.
“This is for the fourth-grade-year-old homeless Jessica,” said McCaskill.
“This is for the little girl that just didn’t care what people thought about her and learned to love herself even though she was really weird.”
Braekhus, who became welterweight world champion in 2009, said: “If this is my last fight, I could leave women’s boxing and just say, ‘I was a part of this. I was a part of taking women’s boxing to this level.'”
McCaskill, also the unified world light-welterweight champion, is now expected to face the winner of the rematch between Katie Taylor and Delfine Persoon on 22 August.
Ireland’s Taylor beat McCaskill by unanimous decision in December 2017 to retain her WBA world lightweight title.