Golden Horn's swan song has been spoiled by Coolmore filly Found in the Breeders' Cup Turf at Keeneland in Kentucky.

Pacemaker Shining Copper blazed a trail but his race was run with half a mile (800m) still to travel, and Frankie Dettori made his move on the John Gosden-trained Prix de l'Arc de Triomphe winner.

However, Ryan Moore was sitting in his slipstream on the Aidan O'Brien-trained Found and despite Golden Horn battling hard, Found flashed past the post with a slender advantage.

Just the third filly to win the race after Pebbles and Miss Alleged - Found had endured a luckless run behind Golden Horn in the Arc, having been second to Gosden's star in the Irish Champion Stakes and the same position at Ascot on Champions Day.

"She's a very special filly, when you think she has run in two Champion Stakes and an Arc, and now this," O'Brien said after the race on Saturday (Sunday AEDT).

"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.

"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."

Golden Horn now heads for stallion duties having suffered just two defeats in his nine-race career - both to fillies, with the other coming behind Arabian Queen in the Juddmonte International at York.

Connections were left to wonder what might have been had the Kentucky track not been hit by a deluge of rain through the early part of the week.

"We always knew we were taking a risk running on ground like this that is softer than anything he's run on before," Gosden said.

"It was too loose for him, but full marks to the filly for beating us fair and square."