Amanda Serrano lambasted Katie Taylor in her post-match press conference after losing to her for a second time on Friday night.
Taylor retained her undisputed light-welterweight title via unanimous decision, though the crowd booed her as they felt she fought dirty.
Serrano was the more aggressive of the two fighters in a pulsating battle but Taylor countered expertly, though she often leaned in with her head.
The 38-year-old, who has lost just three times in 51 fights, threw and landed more punches than Taylor.
Amanda Serrano was defeated by Katie Taylor in their rematch
Reuters
One moment saw Taylor's head collide with Serrano's eye, causing a deep cut that saw blood pour down the Puerto Rican fighter's face.
The Irishwoman was deducted a point for the incident, though she still finished 95-94 on every judge's scorecard to claim victory.
Serrano was furious after the fight, saying: "I knew when it went to the judges it was going to be a little shady.
"Listen, I chose to fight. I went up three divisions.
"I lost in two and I dared to be great tonight.
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"I am the featherweight champion of the world. I want to be great. I only fight the best. It is what it is. I'm a featherweight.
"Every time you get a cut it hurts. You get blood in your eye. She kept headbutting me, but we knew that from the very beginning, the first fight.
"It's not only my fight, she did it with Chantelle Cameron. Listen, I am Puerto Rican. No matter how many cuts, I will fight to the very end.
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Katie Taylor defended against Amanda Serrano well, though was accused of using her head too much
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"I think 100% because she does it [uses head] in every fight. My first cut was with Katie Taylor. She did it with Chantelle Cameron.
"I've seen other fights where she uses her head, dirty. It is what it is."
Serrano did not stop there, taking shots at her rival on social media as well - reposting several replies from fans backing her and hitting out at Taylor for headbutting.
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Katie Taylor retained her undisputed title after beating Amanda Serrano
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After posting a picture of stats that showed her throwing and landing more punches, she wrote: "I landed 107 more punches, she got a point deducted and I lost 95-94 lmfao."
Taylor defended herself after the fight and said: "I definitely didn't agree with the point deduction. I certainly wasn't fighting dirty. Sometimes it gets rough in there."
