Napoli missed the chance to top Serie A after a shock 2-1 home defeat by Parma on Saturday as champions AC Milan hit form with a 3-0 win over Palermo and Inter Milan lost at Catania.
Parma's Francesco Modesto struck the winner against Napoli eight minutes from time after Napoli's Giuseppe Mascara had equalised following Massimo Gobbi's 57th-minute opener.
Milan's Antonio Nocerino, scoring against his former club, Robinho and Antonio Cassano were all on target as Milan cruised past a disappointing Palermo.
Earlier, Inter suffered their fourth loss in their six Serie A matches this season, going down 2-1 at Catania.
Napoli, who host Bayern Munich in the Champions League on Tuesday, looked a pale shadow of the side that had stormed the San Siro two weeks ago in defeating Inter Milan 3-0.
After a lacklustre first half Massimo Gobbi put Parma ahead just before the hour mark, swapping passes with Stefano Floccari before slotting the ball past Morgan De Sanctis.
Napoli, who had created little against a well-organised Parma side, equalised with 15 minutes to go when substitute Giuseppe Mascara slipped the ball under goalkeeper Antonio Mirante after a brilliant flicked pass from Ezequiel Lavezzi.
But Parma silenced the San Paolo faithful with eight minutes left when Modesto tapped in Sebastian Giovinco's enticing cross after a fast counter attack.
Napoli coach Walter Mazzarri felt his players lacked sharpness after returning from international duty.
"Parma played a strong, defensive game," he told Italy's Sky Sport channel. "They looked much fresher. The referee didn't help either by blowing up all the time and breaking our flow.
"It's a shame Lavezzi doesn't score more. He likes dribbling but perhaps doesn't have that coolness in front of goal that's associated with top goal-scorers."
Milan welcomed back the fit-again Robinho allowing coach Massimiliano Allegri to play the attacking trident that hit it off so well last season with the Brazilian playing just behind Swede Zlatan Ibrahimovic and Italian Antonio Cassano.
Cassano, who scored a double for Italy on Tuesday before threatening to quit the game in three years, had two copycat chances to open the scoring after 13 and 18 minutes but slipped the ball the wrong side of the post on both occasions.
Palermo, starting in fourth position after new coach Devis Mangia had inspired several stirring displays, offered little going forward and had keeper Alexandros Tzorvas to thank after 37 minutes when he twice parried fierce Robinho strikes.
The Greek could do nothing three minutes later though when midfielder Alberto Aquilani nodded Ibrahimovic's cross back across goal for Nocerino to tap into an empty net although he would not celebrate against his former club.
Robinho had no such qualms 10 minutes after half-time when he ran on to Ibrahimovic's pass and coolly flicked the ball past Tzorvas as a rampant Milan side cut the Rosanero defence open again.
After having a goal disallowed, the in-form Cassano made it 3-0 in the 64th by side-footing home Ignazio Abate's right wing cross to allow Allegri to rest players ahead of Wednesday's Champions League match at home to Belarus side Bate Borisov.
"The individual talent of Robinho, Cassano and Ibra made the difference," Allegri told Sky Sport channel. "With them all playing together, we were able to create lots of chances. Now we have to keep on winning and climb up the table."
Inter's dismal start to the season continued in Sicily despite the Milan side taking an early lead.
Esteban Cambiasso's sixth-minute volley had given Claudio Ranieri's men the perfect start in a confident first-half display but two Catania goals in the first five minutes of the second half turned the game on its head.
Sergio Almiron bent in a superb equaliser for the home side two minutes after the restart before Francesco Lodi converted a penalty as the Sicilians ran out worthy winners.
Catania have climbed to sixth place with nine points while Inter, who have lost their last two games under new coach Ranieri, have just four points and face the prospect of falling into the relegation zone after Sunday's matches.
"Nobody here's happy to come away without a point," Ranieri told Sky Sport channel. "We got a reaction in the first half but the second was bad. They scored with two breaks. We know we need to get more points on the board."comments