In August he was sent to Goodwood for the Group Three Lanson Champagne Stakes and won by three quarters of a length from the British Horse of the Year Provideo.
Petoski then started favourite for the Champagne Stakes at Doncaster[6] but finished third to Young Runaway, having been unable to obtain a clear run at a crucial stage of the race.
Ridden as usual by Willie Carson he produced easily his best performance to date to win by two lengths from a field which included Jupiter Island (Japan Cup) and Lanfranco (King Edward VII Stakes).
Later in the same month, Petoski was sent to Ascot for the King George VI and Queen Elizabeth Stakes in which he faced a field which included Oh So Sharp and Rainbow Quest from England, Law Society and Princess Pati from Ireland, Treizieme from France, Sirius Symboli from Japan and Strawberry Road from Australia.
Switched to the outside, he produced a strong late run to take the lead in the final strides and win by a neck from Oh So Sharp with Rainbow Quest in third.
Following the race, Dick Hern, who had been confined to a wheelchair following a hunting accident when riding with the Quorn[10] in December 1984, received a personal telephone message from the Queen congratulating him on Petoski's victory.
[11] Petoski was being prepared for a run in the Great Voltigeur Stakes in August when he sustained a pastern injury that ruled him out for the rest of the season.