Inter Milan thrust themselves back into the Serie A title race with a crucial 1-0 win away to city rivals AC Milan at the San Siro on Sunday.
Veteran Argentine forward Diego Milito rolled back the years to score the only goal of the game and move fifth-placed Inter to within five points of their neighbours, who are a point behind leaders Juventus.
The top three picked up only a point between them with Juve's 1-1 draw at home to Cagliari enough to see them take over sole ownership of top spot.
Third-placed Udinese lost 3-2 at Genoa and with fourth-placed Lazio winning there are now just six points separating the top five.
Inter coach Claudio Ranieri said this showed his team are heading in the right direction despite a disastrous start to the campaign.
"We're taking giant steps and that's important, it was important to beat Milan as it was the first match we've won against a direct (title) rival," he told Sky Sport.
"We had three before against Juventus, Napoli and Udinese which served as lessons (they lost all three)."
Milan boss Massimiliano Allegri played down the significance of the defeat.
"It doesn't turn things on their head, it's a day in which the top three picked up just one point so nothing's changed," said Allegri.
"All that's happened is we lost the derby and now Inter are back in the title race."
Milan had much the better of the first period but Inter still looked dangerous when they could get forwards.
They had the ball in the net in the fifth minute but Thiago Motta's header from Maicon's free-kick was rightly ruled out for offside.
Milan came close when Kevin Prince Boateng and Zlatan Ibrahimovic both shot over.
Ricardo Alvarez missed a great chance for Inter when clean through as he dallied and then hit his finish straight at Christian Abbiati.
On the stroke of half-time Inter were saved by the woodwork.
On a rapier counter, Pato teed up Mark van Bommel to crash his shot against the bar, with Julio Cesar well beaten, but the goalkeeper sprawled to his right to keep out Urby Emanuelson's follow-up.
Inter took the lead nine minutes into the second period thanks to great work from captain Javier Zanetti and a crucial error from Milan right-back Ignazio Abate.
Zanetti surged past two players and then crossed to Milito. Abate looked set to cut it out but he missed the ball, allowing the Argentine striker to carry it forwards and slip the ball inside Abbiati's far post.
Yuto Nagatomo came close with a couple of efforts for Inter while veteran substitute Clarence Seedorf and Robinho were both denied by Cesar.
In Turin, Juve opened the scoring on seven minutes with a stunning team goal that involved a mesmerising exchange of passes and culminated in a tap-in for Mirko Vucinic.
But Cagliari drew level two minutes after the break through Andrea Cossu's sumptuous hit from outside the box.
Juve did at least set a record for their longest unbeaten start to a season, surpassing the 17 games they managed in 1949-50.
"We started well, we had chances to double the advantage but we have to be good and clinical in killing off matches," said coach Antonio Conte.
Udinese took the lead in Genoa from a Damiano Ferronetti header but the game changed in a 60-second period at the start of the second half with goals from Andreas Granqvist and Bosko Jankovic.
Genoa extended their lead through Rodrigo Palacio but Udinese set up a grandstand finish when Antonio Di Natale pulled a goal back from the spot after Genoa captain Marco Rossi had been sent off.
"We didn't deserve to lose. It was a great game but we just had three minutes of black-out at the start of the second half," said Udinese coach Francesco Guidolin.
Lazio laboured to a 2-0 win over Atalanta at Rome's Stadio Olimpico to breathe new life into their faltering scudetto hopes, leaving them five points off Juve.