Inter Milan 3-0 CagliariWinter signing Goran Pandev gave them the perfect start after five minutes' play with Argentinian duo Walter Samuel (20) and Diego Milito (47) wrapping the game up for Jose Mourinho's men.
The result ended a six-game unbeaten run for Massimiliano Allegri's Cagliari, denting their hopes of European qualification.
Bologna 0-0 AC MilanAC Milan fell 10 points behind city rivals Inter after an uninspiring goalless draw at Bologna.
A win for Leonardo's men was key to their hopes of keeping the pressure on their great rivals in the race for the Scudetto.
But Milan's failure to find the back of the net - although they went very close hitting the woodwork twice - means athat Milan slip back to 3rd on the table.
Fiorentina 0-1 AS RomaRoma to move second in the table as Mirko Vucinic got the only goal for the game in the 1-0 win at Fiorentina.
The Viola were left empty-handed after one of their most impressive performances of the last few months while Roma extended their excellent run of form to 12 Serie A games without defeat.
Udinese 3-1 NapoliAntonio di Natale scored twice in injury-time to complete a hat-trick for Udinese in a 3-1 victory against previously in-form Napoli.
Di Natale punished his hometown club, who had goalscorer Christian Maggio sent off just before half-time, to give the Bianconeri a first win in eight Serie A contests.
It provided Gianni De Biasi with a first victory since he took charge on December 22, easing the club's relegation fears and enabling them to put behind them the misery of the midweek Coppa Italia semi-final defeat to Roma.
Serie A Top Eight Team Standings
Team Pl W D L Fr Ag Pts Inter Milan 22 16-4-2 48:19 52 Roma 23 13-5-5 38:26 44 AC Milan 22 12-6-4 36:22 42 Napoli 23 10-8-5 32:27 38 Palermo 23 10-7-6 31:26 37 Sampdoria 23 10-6-7 30:31 36 Juventus 23 10-5-8 35:30 35 Genoa 23 10-5-8 36:36 35