Aidan O'Brien's Roderic O'Connor and Godolphin hope Casamento were unable to sustain their challenges as Alain de Royer-Dupre's Reliable Man took the glory in the Prix du Jockey Club at Chantilly.
Roderic O'Connor was in search of a Classic double having won the Irish 2,000 Guineas a fortnight ago, while Mahmood Al Zarooni's Casamento was aiming to repair his reputation after a disappointing display in the Guineas at Newmarket.
Frankie Dettori soon had the latter at the head of affairs, with Roderic O'Connor not far away in the hands of Ryan Moore.
The pair of them were still bang there turning for home but faded tamely in the straight and finished in the midfield.
Reliable Man was ridden more conservatively by Gerald Mosse but quickened up well once straightened up for home, finishing strongly down the outside of rivals to claim Bubble Chic close home.
The strongly-fancied Baraan ran an incredible race to get up for third.
Jean-Claude Rouget's colt was very slowly away and was tailed off at one stage, but finished with a real rattle to grab a place, looking an unlucky loser.
Stan James cut Reliable Man, who was having just his third start having not seen a racetrack until April, to 12-1 from 33-1 for the Prix de l'Arc de Triomphe. The same firm also slashed Baraan to 8-1 from 20s for Longchamp glory.
Victor Chandler cut Reliable Man to 12s from 33s for the Arc on October 2, and trimmed Baraan to the same price from 20-1. Paddy Power gave Reliable Man a 14-1 first-show quote and go 16-1 from 20-1 about Baraan.
John Gosden's Chester maiden winner Colombian ran a blinder to be fourth under William Buick.
Gosden said: 'That was a super run, he's a lovely horse. He is out of a Linamix mare and he is still rather immature, we have spaced his races out.
'I don't usually bring a maiden winner from Chester to the Prix du Jockey Club, and I think he would have loved softer ground like some of the other horses in the race.
'I think he certainly will be a better horse in the future. I will have to wait for the ground and this really was the plan. He is a young horse who has a great future.'
Buick said: 'I'm very, very pleased with that. It was a rough race. We went an even gallop and got racing early in the straight.
'He stayed on well and I think he will be a better horse with some give in the ground. I think he could well stay a mile and a half.'
O'Brien said of Roderic O'Connor, who was a creditable eighth: 'It was very warm today. He got very warm, but I don't want to make any excuses.'
When asked if he thought his charge did not stay the 10-furlong trip, he said: 'It's possible. It's definitely possible. I can't say for sure and we will have a think and see where we go.'
Moore added: 'The pace was all right. I thought it was fair enough. It is a very hot day, though.'
Dettori said of ninth home Casamento: 'He is about a month away from being in top form. He's nearly there but not quite. The race worked out well, but he is just quite not there yet.'