The Recopa is played between the winners of the Copa Libertadores and the Copa Sudamericana, the two most prestigious club tournaments in South America.
The match was played in Southern Brazilian city of Curitiba.
The efforts of Copa Libertadores winners River Plate to tie the match in the second half were halted by a red card to defender Milton Casco at 76 minutes.
Athletico is seeking only its second international trophy in its history.
The second leg will be played in Buenos Aires at the Monumental de Nunez stadium on May 30.
Source: FOX Sport