Amazing Maria added to her surprise victory at Royal Ascot with success in the Falmouth Stakes at Newmarket.
The David O'Meara-trained four-year-old was a 25-1 winner at Ascot in June and backed up that success with this Group One win at Newmarket's July festival.
Ridden by James Doyle, the 17-2 shot overcame early leader Arabian Queen to win by a length.
Euro Charline finished second, followed by the French-trained trio of Fintry, Avenir Certain and Bawina.
"A lot of people thought it might have been a fluke at Ascot, but I could only say what I felt on the day and I felt she was a class filly," said Doyle.
"I didn't want today to get away from that, so I rode her with plenty of confidence and I knew at halfway it was a game of cat and mouse as we were going real steady.
"I knew if I got first jump on them, she's honest and would hit the line well."
O'Meara added: "At Royal Ascot she was the outsider of the field. We didn't think she was without a chance that day - I thought she could maybe be third - but she won it.
"She has now got a Group One win, which is brilliant. It's very special and it hasn't quite sunk in yet.
"I suppose the Prix Rothschild would be the obvious race for her."