The Fugue came up with a perfectly-timed burst to win the Nassau Stakes by a length at Glorious Goodwood.
The John Gosden-trained filly, ridden by Richard Hughes, surged past front-runner Timepiece in the final furlong with stablemate and favourite Izzi Top unable to match her pace.
The Fugue's win was Gosden's sixth Group One victory over the year.
"She showed her class and Richard rode a typically chilly ride. She's smooth as silk," Gosden said.
Hughes was given the ride after stable jockey William Buick preferred Izzi Top, but the 7-4 favourite did not have the burst when it mattered and she finished fourth, with Timepiece (16-1) second and Was (11-2) coming third.
The Fugue, an 11-4 chance, who finished third in the Oaks at Epsom, broke clear with 150 yards remaining and won the feature race for her first victory since the Musidora Stakes at York in May.
Gosden added: "If anyone deserved to win a Group One race, it was her. There is no point talking about the Oaks any more, but it was a pretty horrific affair."
Hughes said: "That's what you call a good spare ride. She's a beautiful filly and she floats across the ground.
"The more I pulled her back, the more she wanted to go - she was like an elastic band ready to quicken."
The Jim Goldie-trained Hawkeyethenoo (9-1) held off Imperial Guest (25-1) to win the Stewards' Cup.