Almanzor sprang a 20-1 surprise to give trainer Jean-Claude Rouget his second win in the French Derby at Chantilly.
Having also won with Le Havre in 2009, Rouget sent out the son of former Prix Jean-Luc Lagardere winner Wootton Bassett, to win by a length and a half.
Zarak came with a late rattle to claim second spot, with Dicton also putting in good late work to take third place, another length and three-quarters away.
Rouget also saddled leading fancy Mekhtaal, but he failed to challenge.
After Harry Dunlop's Robin Of Navan had made most of the running, jockey Jean-Bernard Eyque brought Almanzor through with a well-timed finish.
Following the win, Almanzor was installed as a 16-1 shot for the Prix de l'Arc de Triomphe in October.