Ireland's Katie Taylor (14-0) completed her journey from Olympic gold to undisputed women's lightweight world champion with a thrilling but controversial points win over Belgian Delfine Persoon (43-2).
Bray boxer Taylor, who was the clear favourite going into the bout, came under relentless pressure from the Belgian police officer 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 over the WBC titlist, who had never fought outside of Europe before.
Taylor, described as the closest thing to royalty in her homeland, added Persoon's WBC belt to her IBF, WBO and WBA titles to hold all four belts at 135lbs, as well as the coveted Ring Magazine title too.
Although the underestimated Persoon shook her finger as the decision was read and left the ring in tears with many of the ringside media thinking the Belgian had done enough to claim a shock win, on a night full of surprises.
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 walked forward and applied a pressure Taylor had never before experienced 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, still swinging.
All week Persoon had sounded like a written-off fighter who would throw everything into this and she certainly did.
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 the grandest of stages.
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.
There was a shocker in the headliner as Anthony Joshua (22-1) was stopped by Mexican challenger Andy Ruiz Jr (33-1) in the seventh.
Callum Smith (26-0) floored Hassan N'Dam (37-4) three times in three rounds as he delivered a clinical display to defend his WBA super-middleweight world title.