Udinese ended Leonardo's perfect record since taking over as Inter Milan coach from Rafael Benitez with a 3-1 win over the Italian champions in a lively lunchtime match in Serie A today.
Inter, aiming for a sixth straight win since the Brazilian's arrival in the San Siro dugout, took the lead after a quarter of an hour through Dejan Stankovic. Udinese then stunned Inter with goals from Cristian Zapata and Antonio Di Natale to go into the break 2-1 up, with Maurizio Domizzi adding a third midway through the second half.
The result left Udinese treading water in eighth, although they made up ground to within one point of seventh-placed Palermo, while Inter remain fifth on 35 points, six adrift of leaders AC Milan.
A sixth win here would have seen Inter climb to second and that looked on the cards when Thiago Motta pulled the ball back for Stankovic to fire past Udinese goalkeeper Samir Handanovic in the 16th minute.
Inter, though, barely had time to savour their good fortune when the hosts were back on a level footing. After a failed Inter clearance from a corner the ball fell to Zapata on the edge of the box and the Colombian defender shot into the top corner of Luca Castelazzi's net.
Four minutes later Udinese were in front. And the man responsible was Serie A's top scorer Di Natale, who took his tally to 15 with a superb free-kick which dipped over the Inter wall and out of Castelazzi's reach.
Udinese, recording their first win over their illustrious visitors in 14 attempts, thwarted any hopes Inter may have had of leaving the Stadio Friuli with anything to show for their visit when Domizzi struck in the 69th minute.
Giving his reaction to his first loss in charge Leonardo told Inter's official website: "In football you lose games; it's no big deal. It won't change the way we see things and it won't change the way I see the team.
"We got off to a great start," he added. "Taking the lead at a stadium like this and against a team like Udinese was no mean feat, so I don't think it was a case of us making mistakes or losing our concentration. Perhaps we were a bit tense because of how a few things went. The first half was an evenly balanced affair but Udinese had the upper hand in the second half.
"However, I must say that hardly any of the goals we've conceded from set pieces have been because we were caught out by the opposition; most have been because of a lucky deflection or rebound. So I don't think we have a problem with man-marking at set pieces. Full credit to the opposition - they are capable of hurting any team."