Moonlight Cloud held off the late thrust of Olympic Glory in a pulsating climax to the Prix Jacques le Marois at Deauville.
Turning out just a week after her brilliant display over six and a half furlongs in the Prix Maurice de Gheest, the Freddie Head-trained Moonlight Cloud was buried in behind rivals by Thierry Jarnet as she stepped back up in distance to a mile.
Once given her head a furlong down, Moonlight Cloud's acceleration quickly propelled her into a clear lead and the race appeared to be as good as over.
However, Richard Hannon's Olympic Glory, partnered by Frankie Dettori, really found his stride late on and the two passed the post virtually as one.
After a tense wait, Moonlight Cloud was announced the winner.
The two market principals for the red-hot Group One contest were Jim Bolger's 2000 Guineas and St James's Palace Stakes hero Dawn Approach and Andre Fabre's French Derby winner Intello.
Dawn Approach, turning out 11 days after being beaten by Hannon's Toronado in the Sussex Stakes at Glorious Goodwood, travelled with his usual zest for much of the journey, but when Kevin Manning asked for maximum effort the response was limited.
The chestnut was not given a hard time when his chance had gone and eventually finished fifth, just ahead of his pacemaking stable companion, Leitir Mor.
Intello also moved nicely in the middle of runners and looked a big threat when moving towards the front end under Olivier Peslier.
However, he was unable to keep tabs on Moonlight Cloud and Olympic Glory, finishing an honourable third behind the short-head winner.
Aidan O'Brien's Declaration Of War, behind Dawn Approach in the Sussex, reversed placings on this occasion, running respectably under Ryan Moore in fourth.
Having won the Prix Rothschild over the course and distance a fortnight ago, Elusive Kate looked a major contender for John Gosden and William Buick, but she was another to disappoint in seventh.