Serie A - Round-up: Napoli move second
A 2-0 win for title-chasing Napoli at bottom side Bari made the day worse for fifth-placed Internazionale who lost at Udinese.
Champions Inter, 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.
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 but the Brazilian's new 4-3-1-2 formation showed its first shortcomings with a lack of width in a niggly game.
"We started well but then an Udinese in great form came to the party," former Milan boss Leonardo, who had Julio Cesar, Wesley Sneijder and Diego Milito out injured, told Sky.
"When they play like that, it's difficult for everyone."
Bookings for Cristian Chivu, Ivan Cordoba and Stankovic mean they will all be suspended for next weekend's home game with Palermo, who beat Brescia 1-0 on Saturday.
AS Roma went second on Saturday with a 3-0 win over Cagliari but Napoli leapfrogged Claudio Ranieri's team thanks to Ezequiel Lavezzi and Edinson Cavini scoring either side of the break at increasingly doomed-looking Bari, who were reduced to 10 men.
Lazio, strugglers last term, had a flying start to the campaign but inconsistency has set in for Edy Reja's outfit.
The Romans, who omitted striker Mauro Zarate amid media speculation of a row with Reja and a bid from Juve, led through Sergio Floccari's early goal but Gaston Ramirez and Marco Di Vaio (2) hit back for a Bologna side who continue to make light of the club's ownership problems.
Troubled Fiorentina, who drew 1-1 with lowly Lecce, were missing the banished Adrian Mutu and Juan Vargas after a late-night car crash put the Peruvian's Florence future in doubt.
Mid-table sides Chievo and Genoa drew 0-0 in Verona.