Aidan O'Brien's Yeats was surprisingly beaten at odds-on for the second successive year in the Prix du Cadran as Bannaby sprung a surprise under Soumillon.
Trained in Spain by Mauricio Delcher Sanchez, who saddled Equiano to King's Stand glory at Royal Ascot, the five-year-old just held off Incanto Dream in a desperate finish.
Johnny Murtagh was sending out distress signals early in the straight on the triple Ascot Gold Cup winner and he failed to pick up, trailing home in fifth.
Murtagh said of Yeats: "He just ran badly."
O'Brien was at Newmarket, where he said: "I haven't seen the race yet or had a chance to talk to anyone.
"Maybe the season has just taken its toll on him. We trained him for the big races earlier in the season and it may be that he is best when he is fresh.
"No decision has been made as to whether he stays in training next year."
Delcher Sanchez said of the winner: "It's fantastic to win two Group Ones this season over distances ranging from five furlongs to two and a half miles.
"He'll stay in training next year and will be aimed at the Gold Cup."