ROME (AP) -- Juventus and AC Milan each played to scoreless draws Sunday as the top of Serie A remained unchanged, but Milan standout Zlatan Ibrahimovic was sent off for hitting an opponent and could face a multi-game ban.
In the 64th minute of Milan's match with Napoli, Ibrahimovic slapped his right hand on the side of Salvatore Aronica's face.
Ibrahimovic will miss a difficult game at Udinese next weekend and, if he is suspended for up to three matches, will also miss a match with Juventus on Feb. 25.
"It wasn't violent, so I don't think Ibrahimovic will get more than two matches,'' Milan vice president Adriano Galliani said.
Juventus, which was held 0-0 at home by Siena, leads Milan by one point and has a game in hand.
Third-place Udinese lost 3-2 at Fiorentina, which got two penalties from Stevan Jovetic and a goal from Mattia Cassani.
Also, Roma routed Inter Milan 4-0 in a match postponed by 24 hours due to a rare snowstorm in the capital. Roma's 20-year-old striker Fabio Borini scored twice and Juan and Bojan Krkic also found the net for the Giallorossi.
"The merit belongs to Roma, they really played a great match and we weren't valid opponents,'' Inter manager Claudio Ranieri said after his club's third straight match without a win. "We can't go on like this.''
Elsewhere, it was: Chievo Verona 1, Parma 2; Lecce 0, Bologna 0; Novara 0, Cagliari 0; and Palermo 2, Atalanta 1.
Earlier, a spectacular goal from Rodrigo Palacio in the lunchtime fixture launched Genoa to a 3-2 win over 10-man Lazio.
With his back to the goal, Palacio somehow found the target with a volley over his head into the far top corner in the 10th minute off a corner.
Serbian forward Bosko Jankovic then scored in the 25th and 46th to make it 3-0, but Cristian Ledesma pulled one back with a penalty for Lazio in the 54th and Uruguayan midfielder Alvaro Gonzalez scored again for the Roman club in the 90th.
Lazio defender Mobido Diakite was sent off for apparent protests in the 82nd.
Lazio required seven hours to arrive from Rome and hadn't trained for three days due to the snow in Rome. Still, Lazio remained fourth, trailing Juve by six points.
At the San Siro, Robinho had Milan's best chances but Napoli goalkeeper Morgan De Sanctis was too good.
De Sanctis also denied Ibrahimovic in the 61st and that may have led to the Sweden forward losing his cool minutes later after the referee had stopped play. As players gathered around near the edge of the area, Ibrahimovic moved his arm around another player and hit Aronica.
Ibrahimovic was banned twice for disciplinary incidents last season. First, he was forced to sit out two games for punching a defender in the stomach, then he was banned for three matches for insulting a linesman.
Milan manager Massimiliano Allegri was also expelled Sunday, for protests in the 89th.
Meanwhile in Turin, Siena goalkeeper Gianluca Pegolo was the hero for a series of impressive saves as Juve's Stephan Lichtsteiner, Claudio Marchisio and Alessandro Matri each wasted chances.
Juventus appealed unsuccessfully for a penalty when Siena midfielder Simone Vergassola appeared to stick his hand in the way of a cross from Giorgio Chiellini inside the area in the 85th.
"One episode can change the outcome of a match,'' Juventus goalkeeper Gianluigi Buffon said. "We created that episode and the referee was in a good position but he didn't see it. Sometimes winning or losing is a question of a split second of attention. That can shape a season and that would be a shame.''