Inter Milan [ Images ] suffered their first defeat in six games under new coach Leonardo when the Serie A champions deservedly lost 3-1 at in-form Udinese on Sunday.
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.
Fifth-placed Inter had won five straight games in all competitions since Leonardo replaced Rafa Benitez [ Images ] on December 24 but, despite having a game in hand, they risk slipping nine points behind leaders AC Milan [ Images ] if they beat Cesena later.
The European champions were without injured trio Julio Cesar [ Images ], Wesley Sneijder [ Images ] 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.
Leonardo's new 4-3-1-2 formation also showed its first shortcomings with a lack of width in a niggly game.
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.
AS Roma beat Cagliari 3-0 on Saturday to move up to second, three points above Inter, while third-placed Napoli and Lazio in fourth can put distance between themselves and last term's treble winners with wins over Bari and Bologna later.