Briton Ramla Ali said she fought with "jelly legs" in her points win over Mexican Julissa Alejandra Guzman in Monte Carlo.
Ali, 34, put in a disciplined performance to reclaim the WBA intercontinental title she lost in June, with the judges scoring it 96-94.
Afterwards, she said she had "slept zero hours" the night before the fight.
"I started my period this morning as well. So I was double down on my energy level," Ali said.
Ali, who has nine wins and that single defeat on her professional record, fled war-torn Somalia as a child for Great Britain and has since become an Olympian, activist and model as well as a pro boxer.
"I called for this rematch and I really wanted to prove something - that I'm the better boxer and I feel like I did that tonight," she told DAZN.
"It was a very slow and shaky start for the reasons I just said - but I got my second wind."
Closer to world title shot
Guzman, 26, began as the aggressor against a watchful Ali, wary of the left hook which ended her night five months ago.
Ali landed a terrific straight right hand in the second and again in the third but the bigger, more eye-thudding shots came from Guzman.
A left hook and stinging right appeared to hurt Ali in the fourth but she recovered well, working behind the jab and showing smart movement.
Guzman landed a solid uppercut in the sixth before Ali enjoyed her best round of the fight in the seventh, landing some flush combinations.
She continued to pepper her opponent, doubling up on the jabs. A desperate Guzman, searching for the knockout, was telegraphing her shots as a composed Ali moved in and out of range with more ease in the final two rounds.
"I literally had jelly legs from round one to round 10. It was horrible," Ali said.
Ali's promoter Eddie Hearn described the bout as "make or break" for his fighter and said Ali is moving closer to a world-title shot, potentially against the winner of WBA champion Mayerlin Rivas, of Venezuela, and Mexican Erika Cruz Hernandez, who fight later this month.
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