Thistle Bird, trained by Roger Charlton and ridden by James Doyle, made a winning seasonal debut in the feature Midsummer Stakes at Windsor.
However, the 6/1 chance was forced to survive a lengthy stewards' enquiry after veering left in the closing stages and hampering runner-up Coupe De Ville.
Highland Knight made the running in the extended one-mile Listed race but was collared two furlongs out by Coupe De Ville, who had finished fifth behind Camelot in the 2000 Guineas.
Thistle Bird, sporting a first-time hood, had been given a patient ride by Doyle and she came storming through to outbattle Coupe De Ville by half a length despite failing to keep in a straight line.
Highland Knight plugged on for third with Loving Spirit fourth.
Charlton completed a quickfire double when Rex Imperator landed the following six-furlong handicap.
The 14/1 chance was ridden by George Baker with Doyle on board his better fancied stablemate Zero Money who had to settle for third place at 7/1 with Shropshire (14/1) splitting the Beckhampton pair.