 Ramírez started his career with Sport Boys in 1966 and, in 1968, was the top scorer in the Peruana Primera División.In 1969, Oswaldo "Cachito" Ramirez scored two historic goals against Argentina in the Bombonera (Argentina), that allowed Peru to compete in the 1970 Mexico World Cup, having eliminated Argentina from the competition.In 1970, he joined Universitario de Deportes and won the league title in 1971 and 1974.