The club began to play its matches in División Intermedia (the second division of Argentine football league system by then) at Lanús United old stadium, located in Margarita Wield and General Deheza streets. In 1919 the club got promotion to the top division, Primera División, after beating Argentino de Quilmes. In the first division, Lanús played its first games in the official association, then switching to dissident Asociación Amateurs de Football (AAmF), where the team joined on 8 August 1920, when the squad was defeated by Racing Club by 1–0. That first season in the top division Lanús finished 11th of 20th.