Inter Milan were crowned Italian champions for the 17th time as their nearest rivals AC Milan went down at Udinese.
Inter host Siena later but now know they can no longer be caught at the top of the table, the full-time whistle in Udine sparking celebrations for the Nerazzurri.
The Rossoneri, in contrast, were left to reflect on another disappointing away defeat.
Gaetano D'Agostino put the Bianconeri ahead from the penalty spot in the 31st minute before Cristian Zapata doubled their lead four minutes into the second half.
Massimo Ambrosini scored a consolation for Milan in the third minute of stoppage time but it was too little too late.
With two games of the season remaining, Milan must now look over their shoulders as Juventus challenge them for second place, while Udinese's fifth straight victory keeps them in the hunt for a place in the Europa League next season.
Udinese were Serie A's form team coming into the game.
Striker Fabio Quagliarella has been linked with a move to the newly-crowned champions next season and he gave evidence he would be at home in such a star-studded side as he ran the show for Udinese once again.
He pulled out wide to the right and to the left, causing the Milan defenders no end of problems and providing room for his team-mates at the same time.
In the 22nd minute, he almost put the home team ahead with a header which Dida could only save at the second attempt.
The Bianconeri led just after half-an-hour when Paolo Maldini, playing the 900th game of his career at the heart of the Milan defence, tugged Antonio Floro Flores' shirt inside the penalty area.
D'Agostino sent his spot-kick high into the top left-hand corner of Dida's goal, beyond the Milan goalkeeper's reach.
Simone Pepe went close to adding a second for Udinese early in the second half when his free-kick curled just wide of the post with Dida stranded.
But the home side did not have to wait too long for their second goal, which came in the 49th minute.
D'Agostino's corner from the left was flicked on by Felipe to Zapata, who could not really miss from five yards out.
D'Agostino almost added a third in the 65th minute when he was given the freedom of the pitch before shooting straight at Dida.
Milan did not look their usual selves without the suspended David Beckham and the visitors lacked width, meaning Filippo Inzaghi and Pato up front had very limited service.
They did the best with what they got and Inzaghi almost gave the Rossoneri hope in the last minute when his close-range shot struck the outside of the post.
Ambrosini did find the back of the net in the third minute of stoppage time, but it was no more than a consolation for Milan.
There was still time for Quagliarella to hit a post as he narrowly missed out on the goal his play deserved, but the three points took Udinese back to within three points of sixth-placed Roma with two games remaining.
