Milan: AC Milan lost 2-0 at home to Palermo and failed to move back level with third-place Sampdoria, which beat Fiorentina 3-1 earlier Sunday in Serie A.
Cristian Zapata scored an own goal and was at fault for Paulo Dybala's second as two goals in as many minutes consigned Milan to its second loss of the season.
Milan goalkeeper Diego Lopez also had to pull off a string of fine saves in his first appearance since mid-September.
"This is football," Milan coach Filippo Inzaghi said. "You grow also through games like this. The team gave everything it had. ... We started really well. But everything will help us grow."
Sampdoria goalkeeper Sergio Romero saved a penalty to help his side move three points ahead of Milan and Udinese, which lost 4-2 to Genoa. Lazio can move level with a win at home to Cagliari on Monday night.
Sassuolo was held to a scoreless draw at bottom club Chievo Verona and Atalanta also drew 0-0 at Torino.
Diego Lopez returned from a hamstring injury and was called into action right from the start at San Siro, making a tough one-handed save to deny Franco Vazquez.
Milan also welcomed back young midfielder Riccardo Saponara, but Alex was injured in the third minute and had to be replaced by Zapata, who headed a corner into his own net in the 24th minute.
The Sicilian side almost doubled its lead immediately but Diego Lopez pulled off a fantastic stop to deny Dybala from point-blank range.
However, Palermo and Dybala did have their goal moments later when the Argentine striker shook off Zapata and fired across Lopez and into the far side of the net.
"Paulo is a player who trains with humility and plays with great character," Palermo Coach Giuseppe Iachini said. "He has all the credentials to aim for a future in a top club."
Sampdoria was keen to get back on track after a dip in form had seen it fail to win any of its past three matches.
It took the lead in the 27th minute when Angelo Palombo drove a penalty into the right side of goal after Alberto Aquilani had clumsily pushed over Roberto Soriano.
Palombo gave away a penalty five minutes after converting one when he brought down Khouma Babacar but Gonzalo Rodriguez's spot-kick was weak and Romero managed to smother it.
Luca Rizzo doubled Sampdoria's lead two minutes from the break, dribbling past two defenders at the byline before sending in a low drive to set club president Massimo Ferrero dancing in the stands.
There was still time before the break for Stefan Savic to get Fiorentina back in the match with a towering header from a corner.
Fiorentina was further boosted when Mario Gomez made his comeback from injury, coming on in the 69th minute for his first appearance since September.
But Eder made sure of the points 12 minutes from time with a stunning solo effort, starting his run in his own half and beating three Fiorentina players.
Sampdoria moved a point above Napoli and three behind second-placed Roma.
Genoa is also a point behind Sampdoria and leapfrogged Udinese in the table.
It went into the match full of confidence after inflicting a first defeat of the season on Serie A leader Juventus midweek, but found itself behind after 23 seconds when Antonio Di Natale beat the offside trap to latch onto Panagiotis Kone's assist and record his 199th Serie A goal.
However, two goals in as many minutes saw Genoa on top.
The visitors leveled with a spectacular volley from Giovanni Marchese into the top right corner from outside the opposite side of the penalty area, before howlers from Allan and Bruno Fernandes allowed Iago Falque to pounce from six yards for his first Serie A goal.
Di Natale set up Silvan Widmer for the equalizer four minutes from the break but Genoa restored its advantage nine minutes after the interval when Alessandro Matri fired in off the right upright.
Substitute Juraj Kucka sealed the match two minutes from time with a chip into the top far corner, off the underside of the crossbar.
