Walter Samuel lit the touchpaper on the fieriest of Milan derbies, and stood back as ten-man Inter Milan rode out a controversial 90 minutes to heap further woe on AC Milan coach Massimiliano Allegri with a 1-0 victory.
All eyes had been on Inter striker Antonio Cassano, who had switched sides at the San Siro before the start of the Serie A season, but it was veteran centre-back Samuel who won the game for the Nerazzurri with a headed goal in the third minute.
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Riccardo Montolivo was denied the chance to restore parity courtesy of a controversial call from referee Paolo Valeri, but AC Milan only had themselves to blame for failing to capitalise when Yuto Nagatomo's dismissal put Inter on the back foot for much of the second half.
The 'Derby della Madonnina' traditionally allows both Milan clubs to put their domestic travails on hold in the pursuit of bragging rights in Lombardy, but such a toothless display from the Rossoneri could have more wide-reaching consequences for Allegri.
Serie A champions Juventus needed a late winner from Claudio Marchisio to see off bottom team Siena with a 2-1 win at the Stadio Artemio Franchi on Sunday afternoon.
Andrea Pirlo gave the Bianconeri the lead with an early free-kick, but the league leaders were pegged back in first-half stoppage time by Emanuele Calaio's equaliser.
However, the visitors refused to settle for the draw and secured all three points five minutes from time when Marchisio volleyed home the winner.
Napoli joined Juventus at the top of Serie A with a hard-earned 2-1 win over Udinese at the Stadio San Paolo.
Marek Hamsik gave Walter Mazzarri's side the lead in the 31st minute, but Giampiero Pinzi responded for the Zebrette, who simply would not lie down.
But Goran Pandev restored the home side's lead on the stroke of half time and they defended resolutely throughout the second half to pick up their sixth win in seven Serie A matches, leaving Udinese struggling in the bottom half of the table with only one win all season.
Roma bounced back from their 4-1 defeat to Juventus a week ago to pick up all three points at the expense of Atalanta, winning 2-0 at the Stadio Olimpico.
Erik Lamela and Michael Bradley got the goals as Zdenek Zeman's side responded to recent criticism to edge up the Serie A table.
It was not all easy going, though, and Atalanta were unfortunate not to go in front before the opening goal after half an hour, but their challenge faded after the hour mark when Bradley's goal left them with a mountain to climb. As a result, Atalanta were beaten for the second week in a row to remain in a precarious position near the foot of the table.
Stevan Jovetic's early goal earned Fiorentina a 1-0 victory at home to Bologna. The Montenegrin forward tapped home from close range after the ball broke to him in the seventh minute. Luca Toni also had an effort ruled out for offside as the hosts dominated proceedings.
The win lifted Fiorentina to the verge of the European places with Bologna still in mid-table.
Pescara's mini-revival was ended in emphatic fashion as Lazio ran out comfortable 3-0 winners at Stadio Adriatico.
The hosts had won two and drawn one of their last three matches having opened the campaign with three straight defeats, but had no answers today as Lazio put them to the sword on the back of a rampant first-half display.
A Hernanes free-kick and a brace by Miroslav Klose had the match won inside 35 minutes for the capital club, who remain well on the coat-tails of the league leaders after securing a fifth win from seven games.
Ivo Pulga started started life in the Cagliari hot seat with a 1-0 win - and a first of the season at that - as Nene`s goal 16 minutes from time saw off Torino.
Pulga is an iconic figure in Sardinia having been a back-to-back promotion winner as a player, and he was this week given the task of working some magic on the other side of the touchline following the dismissal of Massimo Ficcadenti.
Catania made it another trip to Sicily to forget for 10-man Parma as goals from Alejandro Gomez and Gonzalo Bergessio sealed a comfortable 2-0 victory.
Without a competitive win at the Stadio Angelo Massimino in their history, Parma were always facing an uphill battle to register their first win in five Serie A outings.