Katie Taylor retained her undisputed super lightweight title in controversial circumstances after landing what was judged to be a headbutt on Amanda Serrano in Texas.
The bout marked Taylor's first defence of her undisputed gold in front of a crowd of over 70,000 spectators in the USA.
Serrano - the unified featherweight champion and a champion at seven different weight classes during her career - started the bout emphatically, landing a serious left-handed strike on Taylor late in the opening round.
Taylor landed a couple of combinations before finding her accuracy in the third but the power of Serrano proved troublesome for the Bray native.
An apparent headbutt from Taylor in the clinch cut her rival open in the fourth in a fiercely fought clash, and blood would poor from the Puerto Rican for the remainder of the fight with both fighters giving their all.
Taylor was then deducted a point for a subsequent headbutt in the clinch, which left Serrano's corner irate.
Headbutt controversy as Katie Taylor accused of 'dirty' boxing
Serrano's coach Jordan Maldonado accused Taylor of 'dirty' fighting as the bout came to its climax when speaking to Ariel Helwani ringside, while Serrano doubled down on the accusation in her post-fight interview.
Every time you get a cut it bothers you," she said.
"You get blood in your eye, it hurts. She kept headbutting me and that's something she has done before. I think 100% (the headbutts were on purpose).
"It's not the first time. She did it to me, she did it to (Chantelle) Cameron. It is what it is. I'm a champion no matter what."
Taylor meanwhile, insisted that she did not fight dirty while opening the door to a third fight with her rival down the line.
'Thank God I won that fight. Congratulations to Amanda - the triple is on," she said.
"She's a hard puncher and a tough warrior. I don't care if the commentary team or the crowd disagree with the result. The only thing that matters is the judges.
"I didn't agree with the point deduction and I certainly wasn't fighting dirty. Sometimes it gets tough in there."
After the fight Serrano took to Twitter to make more claims of dirty tactics from Taylor.
It had been over two years since Taylor and Serrano first clashed in what is widely regarded as the greatest fight in women's boxing history.
Taylor, edged out a narrow split-decision victory over Serrano as they made history by becoming the women to headline Madison Square Garden back in April 2022.
Taylor did subsequently suffer the first loss of her career after that bout - to Chantelle Cameron - but would avenge that loss with a defiant victory against her conqueror to win the undisputed super lightweight championship.
She had also been accused of using her head to her advantage during a meeting with Cameron.
Taylor's second meeting with Serrano featured as the co-main event on Jake Paul's box office meeting with Mike Tyson, which had been shown by Netflix in an unprecedented move.
The bout is reportedly the most-viewed women's fight in boxing history, with Taylor reportedly pocketing $6 million by opting to defend her titles on the card.
