French stars Brametot and Almanzor were completely upstaged by British challengers Eminent and First Sitting in the two feature events at Deauville.
Jean-Claude Rouget's pair of aces were looking to seal their places in some of the autumn's biggest races on a blockbuster of a card for a Tuesday, but instead their performances provided more questions than answers.
Brametot, winner of both the French 2000 Guineas and the French Derby, was considered one of the home team's biggest hopes for this year's Prix de l'Arc de Triomphe prior to his appearance in the Group Two Prix Guillaume d'Ornano.
But after being settled at the rear of the field, he was unable to pick up in the straight and Martyn Meade's stable star Eminent was away and gone after being given an excellent front-running ride from Ryan Moore.
Having finished sixth in the 2000 Guineas, fourth in the Epsom Derby and fifth in the Coral-Eclipse, Meade was ecstatic to see his pride and joy enjoy his day in the sun.
" He had a clear run and showed how good he is. I'm absolutely thrilled," said the Newmarket handler.
"I'm so thrilled for the horse. He's come through some difficult times and been thrown in the deep end, by me I have to say.
"He's sort of struggled a little bit and never had the full running, whereas today he could bowl along and say 'this is me, this is what I want to do'. He did it in great style.
"Beating a dual Classic winner in France is quite exciting stuff."
Asked whether Eminent could come under consideration for the Arc, Meade added: "He could do. We can all dream, can't we? I do think he'd like that distance (mile and a half).
"I know him so well now, so it just depends how he is at home. If it's a possibility then I'd love to bring him back."
Salouen, trained by Sylvester Kirk, filled the runner-up spot.
Connections of Brametot will let the dust settle before committing to future targets.
Sylvain Vidal, racing manager to part owner Gerard Augustin-Normand, said: "We will discuss it with Jean-Claude in the next couple of days or next week.
"We are very disappointed, of course. That's life.
"I think there is maybe something wrong with Brametot. Today he was not the same horse we know."
Almanzor won the French Derby, the Irish Champion Stakes and the Champion Stakes during a brilliant 2016 campaign and although he had been out of action for over 300 days, he was unsurprisingly a warm order to make a winning return in the Group Three Prix Gontaut-Biron.
However, after travelling well enough into the home straight, the response was minimal when Christophe Soumillon asked for maximum effort and he was ultimately well beaten.
Almanzor is also part-owned by Augustin-Normand and Vidal added: "It is the same thing as with Brametot. We need to talk with Jean-Claude in the next few days.
"Today he had no acceleration."
First Sitting, a Listed winner for trainer Chris Wall at Goodwood back in May and most recently third in a Group Three at Chantilly, tracked Almanzor's pacemaker Zafiro before committing for home soon after the turn.
Garlingari finished strongly, but First Sitting held him at bay in the hands of Gerald Mosse.
Wall told At The Races: " The race went well. Gerald got him in a good position, we wanted to be handy. He quickened up well in the straight and put a bit of distance between himself and the others, a bit like he did at Goodwood.
"He's a very willing horse who runs to the line and the others weren't able to catch him, so that's excellent.
"He trained really well for this race. I said to everyone who cared to listen that it's the best we've ever had him and he proved that today and ran out a good winner.
"We'll put him in the Prix Dollar on Arc weekend at Chantilly, that's a Group Two.
"In the meantime he's also engaged in a race in Istanbul, but I'll see whether the owner still wants to do that. Having won this, that might not be as high on the agenda, but we'll see."
David Elsworth's Tisbutadream very nearly completed a big-race treble for the raiding party in the Group Three Prix de Lieurey, but was caught close home by Andre Fabre's Lady Frankel.
Earlier in the day, Jamie Osborne and Dougie Costello combined to land the Listed Prix de la Vallee d'Auge with Pursuing The Dream.