After winning the 1967–68 Serie B title with Palermo, Benetti started his Serie A career in 1968 with Juventus, making 24 appearances and scoring a goal during his first season with the club. However, he did not remain at the club for long, and he joined Sampdoria on loan during the next season. His breakthrough came in the 1970–71 Serie A season, after joining A.C. Milan in 1970, helping the club to three consecutive second-place finishes in the league between 1970 and 1973. During his time at the club, he won the 1972–73 European Cup Winners' Cup, as well as two Coppa Italia trophies during the 1971–72 and 1972–73 seasons, later being named the club's captain, inheriting the armband from teammate Gianni Rivera. He also scored a memorable long-range goal in the Milan Derby against rivals Inter in March 1973.