The 1918 Copa del Rey Final was an association football match between Real Unión and Madrid FC on 12 May 1918, at the O'Donnell Stadium in Madrid. It was the deciding match of the Spanish cup competition, the Copa del Rey. Real Unión beat Madrid FC 2–0 to win their first title. Unión's captain, forward Juan Legarreta, scored both goals. The final was attended by approximately 10,000 spectators.

Renato Petit de Ory, better known by its French name, René Petit, was a Franco-Spanish engineer, known for being a footballer in his youth. He was one of the most popular players in Spanish football in the 1910s, 1920s, and 1930s, playing for Real Madrid and Real Unión, and becoming a member of the France national team. He represented France at the 1920 Summer Olympics in Belgium.