|Di Natale, centre, put Udinese in the lead to give Leonardo his first taste of defeat at his new club [EPA]
Inter Milan fell to their first defeat in six games under new coach Leonardo when the Serie A champions lost 3-1 at in-form Udinese.
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.
Serie A top scorer Antonio Di Natale then curled a superb 25th-minute free kick into the bottom corner and Maurizio Domizzi exposed some questionable goalkeeping from stand-in Luca Castellazzi in the second half.
Fifth-placed Inter had won five straight games in all competitions since Leonardo replaced Rafael Benitez on Christmas Eve.
A 2-0 win for title-chasing Napoli at bottom side Bari made the day worse for the European Champions, who have a game in hand but risk slipping nine points behind leaders AC Milan if their rivals beat Cesena at home later.
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.
"We started the match well and with the right mentality," Leonardo said.
"Unfortunately we couldn't come back, but it is a difficult stadium to come to and Udinese is in great form."
Inter were without injured trio Julio Cesar, Wesley Sneijder and Diego Milito and although they started with the same confidence they have displayed under the Brazilian, the frailty of the short Benitez era soon returned.
Stankovic tested Udinese goalkeeper Samir Handanovic twice and the visitors had a shout for a penalty but the hosts were constantly dangerous with Alexis Sanchez, an Inter target given their wish for an extra striker, always busy.
Roma soothed internal strife by clambering up to second on Saturday with an easy 3-0 home win over Cagliari but Napoli leapfrogged Claudio Ranieri's team on Sunday 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 with two 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.
On Saturday, Francesco Totti netted a penalty midway through the first half after a foul on Daniele De Rossi by Michele Canini and Simone Perrotta doubled the lead in the second half after Juan's header was parried.
Jeremy Menez scored a late third.
Totti's goal followed a spat earlier this month with coach Claudio Ranieri, who according to media reports has also clashed with Mirko Vucinic over the rotation of his strikers.
The Montenegro forward started on the bench after owner Rosella Sensi, who is being forced to sell the debt-ridden club in a long drawn-out process, said he was not for sale amid reported interest from Juventus.
Struggling Catania lost 2-0 at mid-table Parma in new coach Diego Simeone's first game in charge.
The ex-Argentina and Inter Milan player, making his debut as a coach in Europe after winning two titles in his homeland, watched in frustration as ex-Juventus midfielders Antonio Candreva and Sebastian Giovinco scored after the break.
"There were good things and others less so," former midfielder Simeone told reporters.
"The first half was good and also at the start of the second we had chances."
Catania, who parted ways with coach Marco Giampaolo in the week, are 16th but could be dragged further towards trouble after Sunday's main programme of matches.
It was not a totally bad day for Sicily with Palermo, in seventh, scoring late through Cesare Bovo to beat second-bottom Brescia 1-0 and keep their European hopes burning.