Overcoming doubts about the possibility of playing again, Keenor returned to the game with Cardiff as they embarked on the most successful period in their history. They won promotion to the First Division one season after joining the Football League in 1920. Keenor helped the club to the 1925 FA Cup Final, in which Cardiff suffered a 1–0 defeat to Sheffield United. In 1926, he replaced the departing Jimmy Blair as club captain, leading the team to success in the 1927 FA Cup Final later in the season, in which they defeated Arsenal 1–0. Their triumph remains the only time the competition has been won by a team based outside England.