Katie Taylor undisputed lightweight champion after points win over Delfine Persoon
Ireland's Katie Taylor completed her journey from Olympic gold to undisputed women's lightweight world champion with a thrilling but highly controversial points win over Delfine Persoon.
Taylor, who was the 1-20 favourite going into the bout, came under relentless pressure from the Belgian throughout 10 rounds that captivated New York's Madison Square Garden.
After a final round in which Taylor looked totally drained as Persoon took aim, the judges' cards read 95-95 96-94 96-94, earning a majority points win.
It means Taylor takes Persoon's WBC belt and adds it to her IBF, WBO and WBA titles to hold all four at 135lbs.
Persoon shook her finger as the decision was read and left in tears with many of the ringside media thinking the Belgian had done enough to claim a shock win.
Speaking on BBC Radio 5 Live's commentary, Ireland's former two-weight world champion Carl Frampton labelled the decision "disgraceful", while former world heavyweight champion David Haye said Persoon would be "heartbroken".
However, Taylor said: "I felt like I did enough at the start to win the fight. It was very close and she was very strong - it was a fantastic showcase for women's boxing.
"I knew it was going to be the hardest fight of my career but I am born for fights like these. I probably like a bit of a fight too much and I probably should have boxed on the outside a bit more.
"I'm definitely happy to give Delfine a rematch if she wants."
From the opening bell, Persoon - a policewoman in her homeland - walked forward and applied a pressure Taylor had never felt in her 13 professional bouts to date.
The underdog landed a right hand in the second, with Taylor responding with a counter-right, only for her rival to walk through it, swinging.
All week Persoon had sounded like a written-off fighter who would throw everything into this - and boy did she.
Taylor, typically so fast at getting in and out of range, found judgments tricky against the often ragged but relentless work of her rival and when they clinched, Persoon did all she could to rough up the London 2012 Olympic champion.
All three judges' cards had Taylor up at halfway and in the sixth, with Persoon cut and swollen above her right eye, it looked like Taylor had found her range as she slipped left to evade and land an eye-catching left hook.
But Persoon was far from done and a straight right sent Taylor into the ropes in the eighth, leaving the Irish woman hanging on, fatigue pouring out of her.
Going into the ninth, the Madison Square Garden crowd continued to sing Oasis hit Wonderwall which had played between rounds, following the chorus with a colossal roar of approval at what they were witnessing.
And Persoon outworked the champion to win the final round, with Taylor looking exposed as shots rained in - a right hand landing flush as she appeared too tired to hold a guard.
Persoon lost for only the second time in 45 outings, having fought the fight of her life. But Taylor, so often showered in plaudits for being peerless at her weight, showed a grit we had not needed to see before.
It was fitting she won the title in a battle, having made the arduous journey from having to pretend she was a boy to box, to this grand stage.
She now holds all the belts at 135lbs, while American Claressa Shields holds the four titles at 160lbs and, crucially, Norway's Cecilia Braekhus holds all four at 147lbs.
Persoon may want to do this again but if not, a bout with Braekhus, maybe at a catch weight between the two divisions, looks mouth-watering. It would be a bout worthy of topping any bill, one of immense significance in women's boxing and one that could make Taylor even greater than she is now.
Analysis from BBC Radio 5 Live
Steve Bunce: "It was a fight I never thought I would get to see. I thought we would get snippets moving forward but I did not think Katie Taylor could be pushed back for the entire 10 rounds. It was the fight women's boxing desperately needed."
Carl Frampton: "The judges have got it wrong and it is heartbreaking to see Delfine Persoon in tears. I thought she won that fight by miles and that was a disgraceful decision."
David Haye: "That is not the sight you want to see where someone has given everything in the gym but they do not get the decision because of the political power. Delfine Persoon is going to be heartbroken by that."
Promoter Eddie Hearn said: "I had it as a draw, but I was not sure. She (Taylor) boxed well in the middle rounds, and I thought she boxed the wrong fight. Persoon was incredibly strong and Katie Taylor did not look herself tonight.