Francesco Valiani scored a stunning goal as promoted Bologna beat Milan 2-1 at the San Siro yesterday to spoil Ronaldinho's Serie A debut.
Midfielder Valiani blasted the ball home from outside the box in the 79th minute after Massimo Ambrosini had cancelled out Marco Di Vaio's goal for Bologna in the first half.
Last year's runners-up Roma drew 1-1 with Napoli, who had defender Fabiano Santacroce sent off for a second yellow card in the 54th minute.
Juventus also drew 1-1 at Fiorentina in yesterday's late game, which meant none of Italy's big four made a winning start, after champions Inter were held 1-1 at Sampdoria on Saturday.
Former Italy forward Di Vaio, a close-season signing from Genoa, dented the San Siro's excitement at Ronaldinho's debut in the 18th minute with a fine diagonal strike.
The Brazilian had a hand in the equaliser, floating a cross into the area four minutes before the break for Ambrosini to head home.
Ronaldinho went on to create a string of chances that his teammates failed to put away.
One fell to Andriy Shevchenko, who could not find the net with only the keeper to beat at the start of the second half after coming off the bench to mark his return to Milan after two troubled seasons at Premier League club Chelsea.
"Early season surprises can happen when teams that aren't in top condition meet better prepared sides, like Bologna today," Milan coach Carlo Ancelotti told Sky television.
"The impression I had is that this team can do excellent things, perhaps by changing something, maybe the system of play. My optimism derives, above all, from Ronaldinho's performance."
At Rome's Stadio Olimpico, Alberto Aquilani nudged the ball home for the hosts just before the half hour after fellow Italy midfielder Daniele De Rossi had picked him out in the area.
Marek Hamsik knocked in the rebound of his own header on to the crossbar to level for Napoli shortly after Santacroce's sending off.
In Florence, Alberto Gilardino spun away from marker Olof Mellberg to fire into the net and earn the home side a point in the 89th minute.
Pavel Nedved had opened the score in the 39th after his Czech compatriot Zdenek Grygera burst into the box from the right and served an inviting pass from the baseline.
Fiorentina had Felipe Melo sent off shortly before Gilardino's equaliser for a bad tackle on Juve's Cristian Poulsen.
In yesterday's other matches, Torino beat Lecce 3-0 in Turin, Lazio came from behind to beat 10-man Cagliari 4-1 in Sardinia, Atalanta and Catania secured 1-0 home wins over Siena and Genoa, and Chievo beat Reggina 2-1 in Verona.
Those teams join Bologna and Udinese, who beat Palermo 3-1 in their opening game on Saturday, at the top of Serie A.