Hollie Doyle and Trueshan put up a stunning front running performance to land the Group One Prix Cadran on Saturday, the first day of the meeting that climaxes with Europe's most prestigious race the Prix de l'Arc de Triomphe.
It was Trueshan's second win in France's most celebrated staying race, having won it in 2021 when ridde by James Doyle, no relation to Hollie.
Trueshan and Doyle were accompanied for most of the 4000 metres (2.4 miles) contest by Irish raider Emily Dickinson.
However, once Doyle turned for home and saw the winning post in the distance she moved up a gear and Frankie Dettori and Emily Dickinson faded badly.
Nothing could get near Trueshan, who was racing on ground he does not usually appreciate, and Doyle was relaxed enough to wave her whip towards the stands on passing the post.
Doyle, who became the first woman jockey to win a mainstream European classic last year when landing the Prix de Diane (French Oaks), said it was she who decided to set the pace.
"I thought I would take the bull by the horns and ride him like I like to ride to him," she said.
"He loved it I could tell as he pricked his ears.
"I am not going to lie I was quite worried walking the track this morning but he is a class horse and trained by a very good trainer Alan King," added the 26-year-old English woman.
Her ride was roundly applauded as she returned to the winners' enclosure, loudest of all by the horse's part owner Andrew Gemmell.
"What a horse, what a rider!" exclaimed Gemmell.
"I had faith he would adapt to the ground as he is such a durable character, and as for Hollie she showed why she is so respected by her rivals."
- 'Taken revenge' -
Trueshan's colours are not as historic as the Wertheimer's and theirs were carried to victory by Double Major in the opening race the Group Two Prix Chaudenay on an unusual for Arc weekend sun-baked Longchamp.
England also picked up the other Group One prize on offer the Prix de Royallieu, the William Haggas-trained Sea Silk Road taking the honours.
For Haggas it was his second successive win in the race, though, this time it was French jockey Aurelien Lemaitre and not Doyle's husband Tom Marquand who was on board.
"Thankfully we had a calm race, she has a habit of stopping in her races but this time she kept going," said Lemaitre.
"When one has the luck to be called by such a top trainer it says a lot about how one is regarded."
Maxime Guyon guided home Double Major in the Chaudenay, the French jockey relieved the finishing post came when it did.
Irish runner Harbour Wind came with a storming run and would have caught the winner if the race had been a few metres further.
"What a top performance," said Guyon.
"I am happy winning for Christophe Ferland (the trainer) and for the Wertheimers.
"He has taken revenge on several horses today who have beaten him in the past.
"He managed to find an extra gear which is not normal for him as he is usually a dour stayer.
"That is why I went early for the victory, but as one after the other came to challenge him he found that gear and did not crack.
"Thankfully I was unaware of the Irish horse coming so fast but the post came in time."
Guyon was not done for the day as having won the Arqana Criterium he brought up winner number three both for him and England with Poker Face in the Group Two Daniel Wildenstein.
Poker Face was landing his third successive victory for his trainers, Simon and son Ed Crisford.
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