In 1916 the team affiliated to Argentine Football Association and won the Segunda División de Ascenso tournament. In the 1920s the club changed its team to "Club Atlético San Telmo" which has remained to date. In 1926 and due to the lack of a deed of sale, San Telmo had to move to Isla Maciel in Dock Sud district of Greater Buenos Aires. The club inaugurated its own stadium there three years later. The first title won by San Telmo was 1949 Primera C but due to a restructuring of the Argentine league system, the squad did not promote to the upper division.