One Master began her 2019 campaign by running fourth behind Beshaayir in the Lanwades Stud Stakes at the Curragh on 25 May. Starting a 20/1 outsider for the Queen Anne Stakes at Royal Ascot in June she took the lead a furlong out but was overtaken in the closing stages and came home third behind Lord Glitters and Beat The Bank. In the Falmouth Stakes at Newmarket Racecourse on 12 July she produced a sustained run from the rear of the field but failed by a neck to overhaul the Michael Stoute-trained four-year-old Veracious. She was dropped back in distance for the Prix Maurice de Gheest over 1300 metres at Deauville Racecourse in August and came home fifth behind the three-year-old Advertise.
