Winter was denied a fifth successive Group One triumph by Hydrangea, who had finished behind her in the Nassau Stakes at Goodwood.
However, trainer Aidan O'Brien had said Winter had an interrupted preparation and that might have made the difference in a tight finish.
Another O'Brien filly, Roly Poly, made the running with the two stable companions not far behind.
It looked as though Winter's class might prevail, but Hydrangea (20-1) just would not give in for Wayne Lordan and got the verdict over the even-money favourite.
The John Gosden-trained Persuasive was third, with Godolphin's Wuheida fourth for Charlie Appleby.
Lordan said: "She's very consistent and has run well all year. She really likes this track and likes turning.
"It's nice for her, she's been beaten four or five lengths in a number of Group One races this season and now she's had her day.
"I didn't think I'd get there, but she put her head down and she tries very hard."
Hydrangea was the last horse to have beaten Winter when taking the Irish 1,000 Guineas Trial on this course in April and the pair are regular work partners
O'Brien said: "I'm delighted for the filly and I'm delighted for Wayne. She is Winter's work partner all year, and maybe she turned around and said Hydrangea you can have this one today!
"They ran together in the trial before going to Newmarket and Hydrangea pipped Winter, so it was great really.
"She was the only one of the four fillies that had not won a Group One. We felt that Winter was going to improve a bit from the run. She was carrying a little bit of a tummy, but needed to run.
"The winner will stay further. She could go for the Prix de l'Opera.
"Winter is in the Arc, and the Opera is another option."
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