Champions Inter Milan, desperate to make up ground after a poor start to the Serie A season, suffered their first defeat in six games under new coach Leonardo when they lost 3-1 at in-form Udinese on Sunday.
A 2-0 win for title-chasing Napoli at bottom side Bari made the day worse for fifth-placed Inter, who have a game in hand but risk slipping nine points behind leaders AC Milan if their rivals beat Cesena at home later (1945 GMT).
On the plus side for Inter, Lazio, in fourth, lost 3-1 at Bologna and injury-hit Juventus drew 0-0 at coach Luigi Del Neri's former club Sampdoria in a scrappy encounter with Alessandro Del Piero missing a great chance in stoppage time.
Inter's Dejan Stankovic slammed in a 16th-minute opener after Thiago Motta's pass but defender Cristian Zapata soon equalised for eighth-placed Udinese with a powerful left-footed shot which Luca Castellazzi failed to stop.
Serie A top scorer Antonio Di Natale then curled a superb 25th-minute free kick into the bottom corner and Maurizio Domizzi exposed more questionable goalkeeping from stand-in Castellazzi in the second half.
The European champions had won five straight games in all competitions since Leonardo replaced the struggling Rafa Benitez on December 24.