Aidan O'Brien swept the top three at the Prix de l'Arc de Triomphe as 6-1 shot Found swept to victory.
Unbeaten in 2016, Postponed came into the race as the favourite having been handed what was seen as advantageous stall draw of seven.
However, it was reigning Breeder's Cup champion Found who stole the show and surged to victory, the four-year-old filly winning by one-and-a-half lengths over 12 furlongs at Chantilly - hosting the race while Longchamp undergoes redevelopment work.
Second went to 20-1 shot Highland Reel, while 14-1 chance and Gold Cup winner Order of St George came home in third for four-time winner Frankie Dettori.
Dettori was unable to claim back-to-back Arc wins for the second time in his career as Ryan Moore brought Found home in style.
Found had been third last at one point in the race but found the speed to power through the field and prevail by a relatively comfortable margin.
Meanwhile there was disappointment for Roger Varian as Andrea Atzeni could only guide Postponed to fifth behind Siljan's Saga.
O'Brien said afterwards: "We've had our eyes on this for a long time. When Ryan rode her as two-year-old, he said she could win an Arc - he was obviously right."