Brown Panther, the winner of last month's Irish St Leger, was withdrawn from the Canadian International at Woodbine after unseating his rider.
The horse, owned by former England striker Michael Owen, unseated jockey Richard Kingscote in the preliminaries.
"Long way to come for nothing! Thank goodness horse and jockey are both OK," wrote Owen on Twitter.
The race was won by Hillstar, with Just The Judge and Caspar Netscher also victorious to make it a British treble.
Jockey Ryan Moore guided Hillstar to a comfortable victory for Newmarket trainer Sir Michael Stoute in the $1m (£620,000) race .
Just The Judge won the EP Taylor Stakes, while Caspar Netscher took the Nearctic Stakes.
Jamie Spencer, who is due to retire next month, rode Just The Judge to victory for trainer Charlie Hills. The horse will now head to the Breeders' Cup Filly and Mare Turf race at Santa Anita on 1 November.
Caspar Netscher, trained by David Simcock, gave 30-year-old Scottish jockey Andrew Mullen the biggest win of his career.
It was the horse's first victory in more than two years having been retired to stud, only to return to training after been found to be subfertile.