On 19 July, the filly started the 1.4/1 favourite for the Group Three Prix Chloé over 1800 m at Evry Racecourse and won by one and a half lengths from Licara.
[4] Pat Eddery took over from Lequeux for Detroit's next race, the Group One Prix Vermeille over 2400 m at Longchamp Racecourse on 14 September.
She started the 11/4 favourite against a strong field which included Aryenne (Poule d'Essai des Pouliches), Mrs Penny (Prix de Diane), Cairn Rouge (Irish 1,000 Guineas) and Gold River.
Ridden by Eddery, she started the 6.7/1 fourth choice in the betting behind the British four-year-old Ela-Mana-Mou, the French colt Le Marmot and the 1979 Arc winner Three Troikas.
Unusually, the race was run on firm ground and the presence of several pacemakers ensured that the early pace was very fast.
Detroit made rapid progress, overtaking Ela-Mana-Mou and Three Troikas inside the last 200 m and holding the late run of Argument to win by half a length.
In a slowly run race, she accelerated clear of her three opponents early in the straight and was eased down in the closing stages to win by two lengths from Lancastrian, with Gold River in third place.
Detroit was well-placed in the early stages but dropped away in the straight and finished twentieth of the twenty-four runners behind Gold River.
On her only subsequent appearance, Detroit finished fifth behind April Run in the Turf Classic at Aqueduct Race Track.