The Jonathan Pease-trained Act One broke Aidan O'Brien's stranglehold on Europe's Group One juvenile colt's programme at Saint-Cloud in France this afternoon.
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, representing Paul Cole, three quarters of a length away in third.
O'Brien's Mutinyonthebounty and Diaghilev were fourth and fifth respectively.
The Ballydoyle handler shrugged: "We were beaten by a very good horse on the day."
He plans to be back in Paris next weekend for the last remaining European Group One - the Criterium de Saint-Cloud, which if he wins will give him a world record of 23 Group One wins in a season.
Act One, owned and bred by Gerald Leigh, benefited from a positive ride by Thierry Gillet, who had the son of In The Wings (2.4-1) tracking Clive Brittain's Halawellfin Hala (who finished last) until hitting the front early in the straight. This was a first Group One for Gillet.
Pease was full of praise for his jockey, and his mount, who the Chantilly-based Briton reckons will take the step up to a mile and a half in his stride next term.
Pease said: "It's a dream to have a horse like him - he reminds me a little of Tikkanen (his Breeders' Cup winner)."
Act One is now unbeaten after three outings, and on this evidence has a bright future ahead.
The supporting Group Three Prix Perth went to the French-trained Keltos, with Cole's Cornelius in second and May Ball, trained by John Gosden, third.