Elusive Kate completed back-to-back victories in the Prix Rothschild with a fluent success at Deauville.
Winner of a controversial race for the Falmouth Stakes at Newmarket's July meeting, the John Gosden-trained filly was far too good for her rivals in France.
She stormed to victory in the hands of William Buick, with Duntle edging out for second place.
The Jane Cecil-trained Chigun made the early running under Tom Queally, but Elusive Kate was hot on her heels from the start.
Buick kicked on some way out and the 5-2 favourite soon had the rest of the field trailing in her wake.
Duntle made good late progress to take second place, just ahead of Kenhope, with Topaze Blanche fourth.
Gosden said: "She handled the ground well - she can run on most ground - and we are delighted with her run."
Elusive Kate was winning for the fourth time from five starts at Deauville.
Gosden told At The Races: "She handled the ground because they had a biblical proportion tornado last night which caused them to cancel the last three races.
"The breeze got up this morning and the ground was slow, but she handled it well.
"She was third there in the Jacques le Marois last year behind some pretty smart horses. That race is a possibility.
"We'll have a look, but the other thing is she could go for the Matron Stakes.
"I think the plan will be to breed from her next spring."