[1] Born in San Sebastián, Sansinenea found his way into the home of a very prominent club in the capital, Madrid FC, with whom he played for 5 seasons (1916–1921).

At the club he formed a great attacking partnership with Sotero Aranguren and René Petit, and the highlight of his career came in the 1917 Copa del Rey, being one of the most outstanding players in the tournament with a total of four goals, including the winner in the semi-finals against España FC, although he failed to score in the final against Arenas de Getxo as Madrid won 2–1.

Unfortunately, he did not participate in the subsequent 1921 Copa del Rey campaign, which ended in a 1–4 loss to Athletic Bilbao in the final.

[5] Sansinenea missed the previous edition in 1917 because the tournament coincided with the 1917 Copa del Rey Final between Madrid FC and Arenas, which prevented the Madrid national side from using the Madrid FC players, so Sansinenea showed all his class in the 1918 edition, which basically consisted of a two-legged final against Cantabric, and he scored a goal in both games (3–2 and 3–1 victories), thus contributing decisively in the capital side's triumph.

[6] With these two goals, he was the joint-top scorer of the tournament alongside Senén Villaverde and teammate Ramón Olalquiaga.