Goals from Dejan Stankovic, Diego Milito and two from Samuel Eto’o helped the champions to a comfortable win at the San Siro as the Nerrazzuri moved into fourth place, eight points behind AC Milan with a game in hand, to continue Leonardo’s great start as manager.
Elsewhere, Napoli failed to keep up the pressure at the top as Fiorentina held them to a 0-0 draw.
Sunday’s big games see leaders Milan travel to Lecce, and Lazio host Sampdoria.