The daughter of Derby hero Ruler Of The World stormed home to cause a 14-1 shock in the Newmarket feature on Friday.
Joseph O'Brien's filly had been beaten twice since making a winning debut at Killarney in July.
However, she was always travelling strongly under jockey Wayne Lordan and she quickened up well between runners approaching the final furlong.
The 5-2 favourite Hermosa had no answers in the closing stages and had to settle for second, with Pretty Pollyanna running creditably in third on her first try at a mile.
The result gave 25-year-old O'Brien his first Group 1 winner in Britain.
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He said: "I couldn't say we expected her to win, but we always loved the filly and we expected her to run well.
"She did it well and Wayne gave her a great ride. She travelled well and I thought she quickened up well. We're delighted.
"She ran well in the Curragh in a very messy race and then got drawn almost widest of all at Leopardstown, so on her last two runs she never got a fair crack at it really.
"Today was a fairly-run race and she showed how good she is."
The filly was cut into 16-1 for the 1000 Guineas next May, but her trainer views her as a potential Oaks contender, for which she is a best-priced 20-1.
O'Brien continued: "She's definitely well entitled to line up in it (1000 Guineas).
"Being by Ruler Of The World, she's probably more of an Oaks filly, but we'll get today out of the way and worry about that when the time comes.
"We'll enjoy today and give her a nice break through the winter and dream about next year."
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