The Fugue, ridden by William Buick, denied star French filly Treve victory in the Prince of Wales's Stakes at Royal Ascot.
John Gosden's mare bided her time while Prix de l'Arc de Triomphe winner Treve was well back as Elkaayed set the pace.
But The Fugue quickened up nicely and Treve, under Frankie Dettori, could not respond leaving Buick victorious ahead of Magician (6-1) with Treve third.
It was a fourth Group One win for the 11-2 shot, owned by Lord Lloyd-Webber.
The first three finishers all broke the previous course record for the one mile and two furlong trip.
Gosden's mare had won both the Yorkshire Oaks and the Irish Champion Stakes last season before finishing second in both the Breeders' Cup Turf and Hong Kong Vase, before a trip to Meydan for the Dubai Duty Free in March proved disappointing.
But she showed great determination to bounce back, much to the delight of Buick and trainer John Gosden.
"She's been an absolute star for me and everybody back at the yard," said Buick. She proved today what she can do against top-class horses.
"When she gets an uncomplicated run like she did today and they come back to her, she's lethal, like she was there. It means everything to everyone involved."
Dettori admitted afterwards that he had concerns about Treve from an early stage.
"Going to the start she didn't feel like Treve and at the back of my mind I knew then I was in trouble," he said.
"I was hoping in the race she would loosen up and warm up, but I knew my fate at the three-furlong marker. She ran a good third, but it's not the Treve we all know.
"Something is definitely wrong and what's wrong was before the race."
Earlier, jockey Pat Smullen landed a double when 9-2 joint favourite Mustajeeb won the Jersey Stakes before Anthem Alexander held on to take the Queen Mary Stakes.
In the Jersey Stakes, the winner and fellow joint favourite Muwaary were up at the front early but it was Mustajeeb who settled the better and was able to stay ahead of his rival, also owned by Sheikh Hamdam Al Maktoum.
Anthem Alexander, trained by Eddie Lynam, made a sluggish start but once she got into gear she looked good and held on despite the efforts of Tiggy Wiggy and Newsletter.