After moving to Italy, Sormani made his Serie A debut with A.C. Mantova in 1961, spending two seasons with the club (1961–63), where he displayed his talent and potential, earning the nickname "the white Pelé". He subsequently attracted the attention of larger clubs, and he moved to A.S. Roma for the 1963–64 season, for an at the time world record of 500 million Lire in 1963, in addition to 250 million more, including the value of the three players Mantova received from Roma in exchange: Torbjörn Jonsson, Elvio Salvori, and Karl-Heinz Schnellinger. During the single season he spent with the capital club, he won the Coppa Italia, although he was unable to display consistently the talent he had demonstrated whilst playing at Mantova. After a difficult season, Sormani spent the 1964–65 season with U.C. Sampdoria, where he also struggled, before moving to A.C. Milan in 1965, where he flourished, and achieved notable domestic and international success. During his time at Milan, he finally fulfilled his potential and established himself as one of the league's top players, winning the 1967–68 Serie A title, the Coppa Italia during the 1966–67 season, the 1967–68 European Cup Winners' Cup, the 1968–69 European Cup, and the 1969 Intercontinental Cup.