The Jonathan Pease-trained Act One broke Aidan O'Brien's stranglehold on Europe's Group One juvenile colts' programme at Saint-Cloud on Saturday.
O'Brien, whose Ballydoyle youngsters had captured all eight of the top two-year-old races held so far this season, fielded three in a bid to make it nine out of nine - his squad headed by the Dewhurst Stakes second Landseer.
With Mick Kinane up the odds-on shot burst through a gap close home but too late to peg back Act One, the sole French runner in the field after the defection of Andre Fabre's Bernebeau with a last-minute injury.
Half-a-length was the difference on the line, with Guys And Dolls three-quarters of a length away in third.
Mutinyonthebounty and Diaghilev, O'Brien's other pair, were fourth and fifth respectively.
O'Brien said afterwards: "We were beaten by a very good horse on the day." He plans to be back in Paris next weekend for the the Criterium de Saint-Cloud, which if he wins will give him a world record of 23 Group One wins in a season.
Officer, putting in a quick reappearance after a Breeders' Cup Juvenile failure, came unstuck again in the California Cup Juvenile Stakes at Santa Anita on Saturday.
The Bob Baffert-trained runner edged to the front only for Yougottawanna to take his measure by a length and a half in the extended mile test.
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