Third-placed Palermo was held to a 0-0 draw at Parma on Sunday, dropping the Sicilian club further behind Italian league leader Inter Milan and AS Roma.
Palermo hasn't won in five games in any competition.
Inter beat Siena 2-0 on Saturday, matching a 97-year-old club record with its 11th consecutive win in all competitions. Second-placed AS Roma beat Atalanta 2-1 for its sixth straight league win.
Inter leads with 36 points, followed by Roma with 32 and Palermo with 28.
Parma's goalkeeper Luca Bucci denied several late scoring chances for Andrea Caracciolo.
Injury-depleted AC Milan also continued its poor form, drawing 2-2 at Cagliari.
Milan were forced to play the final 15 minutes with 10 men after Andrea Pirlo was sent off for taking down David Suazo from behind.
Cagliari dominated the first half but Milan went ahead three minutes after the interval with a header from Alberto Gilardino.
Cagliari equalized with a penalty by Suazo in the 53rd, then went 2-1 up through Andrea Capone's first goal of the season in the 65th. Marco Borriello equalized for Milan in the 70th after controlling the ball on his chest, followed by a bicycle kick.
Gionatha Spinesi scored a 79th-minute equalizer for Catania in a 2-2 draw with Ascoli. Catania moved into a tie with Livorno for fourth place, while Ascoli remain the only winless team in Serie A.
Catania goalkeeper Armando Pantanelli pushed a penalty kick by Gaetano Fontana wide in the 10th minute but Sasa Bjelanovic scored from the ensuing corner, although replays showed he was offside. Bjelanovic scored again in the 39th from a header.
Defender Lorenzo Stovini slotted the ball into an empty net for Catania in the 53rd after Ascoli keeper Gianluca Pagliuca was drawn out of position. Spinesi's equalizer came from a header.
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