His performances eventually drew the attention of Celta de Vigo, then in the Segunda División, who signed him in 1933, thus becoming the first Mexican footballer in the club's history.
In total, Díaz de León scored 8 goals in 30 games in two seasons for Celta before leaving in 1935, returning to Eiriña CF.
In gratitude for the magnificent disposition of the Pontevedra team, Celta played a free match in their field, in which Pirelo occupied the midfielder position.
[7] In Celta's first year in the first team, Pirelo was practically undisputed, playing 19 games out of 22, at a time when substitutions did not exist.
[1][5] On 23 April 1941, Pirelo had the honor of forming the Celta eleven that defeated Deportivo de La Coruña 8–0 in Balaidos in the second leg of the round of 32 of the 1941 Spanish Cup;[1] Celta went on to reach the semifinals after beating Real Madrid in the round of 16 and Real Oviedo in the quarterfinals.