Francesco Valiani scored a stunning goal as promoted Bologna beat AC Milan 2-1 at the San Siro on Sunday 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 AS 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 Sunday's late game, which meant none of Italy's big four made a winning start, after champions Inter Milan 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 team mates 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 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."
Mourinho's Inter held
Earlier, Gennaro Delvecchio earned Sampdoria a 1-1 draw on Saturday to deny new Inter Milan coach Jose Mourinho a winning start in Serie A.
Midfielder Delvecchio tucked the ball away for the home team in the 68th minute after Daniele Franceschini headed Marco Padalino's cross into his path.
Earlier, Sweden striker Zlatan Ibrahimovic gave Inter the lead in the 33rd when he brought the ball down with his chest and found the far corner of the net after a one-two with Brazilian midfielder Mancini.
Striker Antonio Cassano wasted a good chance to put Sampdoria in front three minutes after Delvecchio's equaliser, his ball control letting him down when clean through on goal.
Inter keeper Julio Cesar then produced a fine save from a powerful Angelo Palombo shot in the closing stages.
Mourinho, who took charge of the champions after Roberto Mancini was sacked in the close season, had to play midfielder Esteban Cambiasso at centre back because of an injury crisis.
Napoli hold Roma
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 equalizer for a bad tackle on Juve's Cristian Poulsen.
In Sunday'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.