Fancy Blue took the Nassau Stakes at Goodwood to give 22-year-old trainer Donnacha O'Brien a Group One winner with his first British runner.
The 11-4 shot, ridden by Ryan Moore, prevailed as Tom Marquand closed on runner-up One Voice, with Nazeef third and favourite Magic Wand unplaced.
O'Brien, son of legendary trainer Aidan, was a Classic-winning jockey who retired from riding 20 months ago.
Earlier, Moore won the Gordon Stakes on Mogul (9-2) for Donnacha's father.
Mogul, who was sixth in the Derby, beat runner-up Highland Chief with Epsom fifth English King -ridden by Frankie Dettori - back in fourth after struggling to find room.
Donnacha only sent out his first winner in February, but claimed a Classic success as a trainer when Fancy Blue landed the French Oaks earlier in July.
After watching from home in Ireland, he indicated the Prix de l'Arc de Triomphe could be an option later in the season.
"She's unbelievable. You never expect in your first year to get one like her," he said.
Prize money boost
Just before the big contest, racing was given a prize money boost - aimed at helping trainers and owners who have been hit by cuts because of the coronavirus pandemic.
The Horserace Betting Levy Board, which helps fund the sport, says its contribution in the final four months of the year is set to rise by 50% on the originally allocated sum - with £26.2m being provided.
It means that minimum prize money values will increase at all levels from September, with most middle-tier and grassroots races returning to pre-Covid levels.
The revised fixture list for September through to the Christmas period has been announced by the British Horseracing Authority, with a maximum of five meetings scheduled a day, and cards generally comprising of seven races.
Jockeys will still be limited to riding at one race meeting on any day as part of Covid-19 protocols.