Darío Pereyra started his career at the Nacional de Montevideo and debuted at the Uruguay national squad when he was only 18, becoming the captain of the national team at 19. After having scored 14 goals in 34 matches for the Nacional, São Paulo F.C. hired him on 17 October 1977 for 5 million cruzeiros, the second largest sum to be ever paid for a player at the time in Brazil. He arrived at the Congonhas airport wearing a São Paulo jersey, and was received warmly by the supporters of that team. Pereyra was not able to play immediately after his arrival, for he did not have the necessary documentation to do so. In December 1977, Real Madrid C.F. made an offer that could have cut his São Paulo career short, but the player was not interested in playing in Spain at that particular time.