Roly Poly just held off British raider Seafront to take Group Three honours in the Grangecon Stud Stakes at the Curragh.
Ryan Moore had to be at his strongest to get the Aidan O'Brien-trained filly home from James Tate's challenger.
The pair had the race to themselves after Ellery Lane had set the early pace.
Seafront took a narrow lead but Roly Poly (3-1 favourite) was soon on his case and pulled out that bit extra to land the spoils by a neck and bounce back quickly after finishing eighth to Lady Aurelia in the Queen Mary Stakes at Royal Ascot.
The win provided O'Brien and Moore with a Group-race double after Sir Isaac Newton's win in the Finlay Volvo International Stakes earlier on the card.
O'Brien said: "The little bit of extra distance may have suited her. It's not that long after Ascot, but she's a hardy filly. It was a tough performance and you would have to be happy.
"She's a very important filly as a Group winner with her pedigree.
"She could go for the Debutante if we want to try her over seven furlongs."