Also known as "Pierino the pest", Prati began his career playing in Serie C1 with Salernitana, winning the title and promotion to Serie B during the 1965–66 season. He is mostly remembered for his highly successful and prolific stint with Italian club A.C. Milan under manager Nereo Rocco in the 60s and 70s, during which he achieved great international and domestic success, winning a Serie A title, a European Cup, two Cup Winners' Cups, an Intercontinental Cup, and two Coppa Italia titles, forming an excellent partnership with Gianni Rivera.