Injury-hit Serie A leaders AC Milan were unlucky to be held to a 0-0 draw at home with Lazio on Tuesday after missing several chances, giving their title rivals a boost ahead of the rest of the midweek programme.
Midfielder Urby Emanuelson wasted a great opportunity in the first half and Zlatan Ibrahimovic hit the frame of the goal twice from distance after the break.
Antonio Cassano was then brought on to replace fellow attacker Alexandre Pato but the Italy man failed to produce the magic of recent weeks and the Rossoneri only extended their advantage over Napoli in second to five points.
Napoli head to Chievo on Wednesday looking to profit from Milan's slip while fourth-placed Inter Milan, 10 behind their city rivals, visit bottom side Bari on Thursday.
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