Tony Bin
At Doncaster Racecourse on 10 September, Diminuendo was matched against colts for the first time in the St Leger Stakes over fourteen and a half furlongs. Ridden by Walter Swinburn (Cauthen was injured), she was made odds-on favourite, but was beaten a length by the colt Minster Son. She was expected to be retired after the Leger, but Cecil allowed the filly to travel to Longchamp Racecourse for the Prix de l'Arc de Triomphe, for which she was well-fancied despite an unfavourable draw. After reaching fourth place early in the straight she faded in the closing stages and finished tenth behind Tony Bin.