Italy international Luca Toni scored twice to earn Fiorentina a hugely impressive 3-1 win over AC Milan which left the clubs level in second place in Serie A yesterday.
Leaders and champions Juventus, who won 4-1 at Roma on Saturday, are on 33 points, five ahead of Milan and Fiorentina.
Inter Milan are fourth, a further five points adrift, after beating Parma 2-0 at the San Siro with goals from Luis Figo and Argentine Esteban Cambiasso.
Surprise packages Livorno are fifth following a 2-0 win over Empoli.
Toni, Serie A's top scorer, put Fiorentina in front in the 10th minute when he was left unattended by the Milan defence to nod in a Manuel Pasqual free kick at the back post.
Milan, who had won their previous eight Serie A matches, fought back 15 minutes later when Alberto Gilardino's glancing header from Serginho's cross sent them in level at the break.
Just 35 seconds after the restart Martin Jorgensen restored Fiorentina's lead after Milan's Italy international defender Alessandro Nesta failed to deal with a cross from Pasqual and the Dane slid the ball home.
Milan thought they had grabbed an 85th-minute equaliser through Gilardino but the striker's effort was ruled out for a foul on Marco Di Loreto and two minutes later the game was over.
Toni struck with another stooping header, his 15th goal of the season, to give Fiorentina, who only avoided relegation on the last day of the season, a win that raises hopes of a return to the Champions League.
Fiorentina coach Cesare Prandelli praised the way his side had coped with Milan.
"We were up against one of the top teams in Europe and so we were never going to put them under pressure for 90 minutes. We suffered at times, but we did what we had to do and I am very pleased with what the lads achieved," Prandelli said.
Aimo Diana and Francesco Flachi earned Sampdoria a 2-0 win over Lazio, and Palermo fought back from two goals down to draw 2-2 at Treviso.