Internazionale made a stuttering start to their title defence, while promoted pair Genoa and Napoli both suffered defeats.
Ivan Cordoba scored a last minute own goal as Inter were held at home by Udinese, who had gone behind inside the first ten minutes when Dejan Stankovic struck.
Inter played most of the second half with ten men after goalkeeper Julio Cesar was shown a red card for deliberate handball.
Milan made a fine start to their season with three first-half goals in an away success against Genoa.
Massimo Ambrosini scored on 21 minutes and the points were wrapped up before half-time when Kaka opened his account (44) and doubled his tally from the penalty spot a minute later.
Napoli also lost at home as Alessandro Matri (49) and Pasquale Foggia (59 pen) scored second-half goals for Cagliari.
Fiorentina picked up three points from their opener against Empoli as they won 3-1 at the Stadio Artemio Franchi.
Goals in quick succession from Giampaolo Pazzini (55), Adrian Mutu (63) and Riccardo Montolivo (70) give the Viola victory, with Luca Saudati scoring a late consolation for Empoli.
Vincenzo Montella's 86th minute strike secured Sampdoria a 2-1 away win against Siena after Daniele Corvia (68) had cancelled out Claudio Bellucci (34).
Parma drew 2-2 with Catania at the Stadio Ennio Tardini, with all four goals coming inside the first 45 minutes.
Takayuki Morimoto netted the first for Catania on 12 minutes but Andrea Pisanu levelled (27) before Marco Rossi put Parma in front (42). However, the home side led for only a matter of seconds as Davide Baiocco responded for Catania.
Reggina and Atalanta also shared the points with Cristiano Doni scoring from the spot (85) after Nicola Amoruso had put Reggina ahead in the 76th minute.
Roma began their campaign with a 2-0 win at Palermo in the evening kick-off.
The Giallorossi were in control from the off with defender Philippe Mexes firing them ahead just four minutes in.
Alberto Aquilani doubled their lead in the 28th minute, an advantage that proved too great for Palermo to overcome.