The Bluebirds and Pompey first met at a very modest level - the Second Division of the Southern League in 1911/12, the second year of Cardiff City's professional existence. Portsmouth had been relegated from the Southern League First Division at the end of 1910/11, and the two clubs first played each other in a 0-0 draw at a primitive Ninian Park on October 21^st 1911 in front of just 3,500 spectators.

Portsmouth went back up that season and City followed them a year later, so by 1913/14 both clubs were in the First Division of the Southern League, the strongest competition outside the two divisions of the Football League. When City and Pompey met in 1919/20, the first post-World War One season, Portsmouth went on to win the Championship while City finished fourth. But the Football League had already decided to expand their two divisions by adding a third, and they took in the existing Southern League First Division.

The Bluebirds, however, had already decided to apply for election to the Football League Second Division based on their existing and potential support. City were successful in their bid, and were elected to the Football League's Second Division for 1920/21, making the most of their election by winning promotion to top level at the first time of asking. Meanwhile Portsmouth and the rest of the Southern League First Division became the new Football league Third Division.

City and Pompey eventually met in Football League competition in 1927/28 in the original First Division, Pompey having come up from Division two in 1927 while City were winning the F.A. Cup.