Ballydoyle's Found spoiled Golden Horn's swansong when denying him victory in the Breeders' Cup Turf at Keeneland.
Pacemaker Shining Copper blazed a trail but his race was run with half a mile still to travel, and Frankie Dettori made his move on Derby and Arc hero Golden Horn at that point.
However, Ryan Moore was sitting in his slipstream on the Aidan O'Brien-trained ned Found and despite Golden Horn battling hard once headed by the filly, the winner stuck to her guns and flashed past the post with a slender advantage.
Found had endured a luckless run behind Golden Horn in the Arc, having been second to John Gosden's colt in the Irish Champion Stakes and occupying the same position at Ascot on Champions Day.
O'Brien said: "She's a very special filly, when you think she has run in two Champion Stakes and an Arc, and now this.
"To do it all in a month is remarkable. She was drawn badly in the Champion Stakes (at Ascot), and although she came out of it well, I thought the lads' decision to come here was a little bit far fetched to be honest, but she didn't have any luck in any of her races.
"I take my hat off to them for running her. At the start of the season, I did think she was the one for the Arc, but today she has more than made up for that and Ryan has given her a super ride."
Coolmore partner Michael Tabor said: "At the beginning of the season Aidan was adamant this was our Arc filly. She didn't get the rub of the green, but with Aidan when he says something it always comes right in the end.
"When Aidan says something eventually it will happen as he knows the difference."
Dettori said of Golden Horn: "I was happy where I was, but he couldn't pick up on that ground, in fact he laboured on it."
Gosden added: "It was too loose for him, but full marks to the filly for beating us fair and square.
"I said to everyone beforehand that after all the rain and three inches of it it would be far from ideal and the winner is bred to enjoy it more than us.
"Frankie said he was spinning his wheels all the time, but he appears to be bright after his race.
"It has been a long year and thank God we have had a European one-two."