Rosallion followed up victory in the Irish 2,000 Guineas to land the St James’s Palace Stakes for trainer Richard Hannon.
The 5-2 chance came with a late burst under Sean Levey to deny the Aidan O’Brien-trained Henry Longfellow, with French Guineas victor Metropolitan in third.
“I’ve always had great belief in the horse and hoped that when people say your name, they remember the horse along with it,” said Levey.
Rosallion was second in the English Guineas to Notable Speech, who came into the race unbeaten and seeking a fifth consecutive win but finished seventh of the eight runners.
Asfoora (5-1) was ridden to victory by Oisin Murphy for Australian trainer Henry Dwyer in the King Charles III Stakes.
It was the sixth time the five-furlong sprint had been won by a horse from Down Under.
Charyn won the opening Queen Anne Stakes as French challengers Big Rock and Facteur Cheval were unplaced after racing alone on the far side.
The 100-30 favourite, trained by Roger Varian, gave jockey Silvestre de Sousa another big victory after his return to Britain earlier this year, having won the 1,000 Guineas with Elmalka last month.
The three-time champion jockey was given a 10-month ban by Hong Kong authorities last year for breaching betting rules.