Milan: Cristiano Ronaldo scored twice but champions Juventus had to settle for a point as a late Gervinho double snatched a 3-3 draw after promoted Parma staged an impressive comeback in Serie A on Saturday.
Juventus' dropped points allowed Napoli to cut the gap on the leaders to nine points after a confident 3-0 win over Sampdoria.
Massimiliano Allegri's side had already had their confidence shaken after a 3-0 defeat to Atalanta shattered their hopes of winning a fifth straight Coppa Italia.
Saturday's draw was not the response Allegri had called for ahead of their Champions League last 16 first leg tie against Atletico Madrid on 20 February.
"I'm happy for the goals but not the result," said Ronaldo.
"Parma didn't do anything special, they waited for us to make a mistake.
"But we're not worried, we know it will be a great season for Juventus."
Juventus, hit by injuries to defenders Leonardo Bonucci, Giorgio Chiellini and Andrea Barzagli, have now conceded six goals in their last two matches.
But they still have a comfortable nine-point lead over Napoli with Inter Milan 20 points behind in third.
"It doesn't change anything, but we must not take anything for granted," said Allegri.
"We were too light in defence. It was the first time this back four had played together."
Juventus lined up with an inexperienced back line of Leonardo Spinazzola alongside Uruguay defender Martin Caceres who got his first start since moving from Lazio.
Sami Khedira rattled the post twice before Ronaldo opened the scoring after 36 minutes with Daniele Rugani again scoring for the hosts on 62 minutes.
An Antonino Barilla header clawed one back for Parma two minutes later before Ronaldo completed his brace to return to the top of the Serie A goalscorers' chart with 17.
But Ivorian Gervinho threw his side a lifeline on 74 minutes and grabbed a point at the death for Parma who remain 12th in the table, 31 points behind Juventus.
"At least we satisfied those who complained we weren't entertaining," said Allegri.
"But the beautiful football doesn't pay off, at the end of the day you have got to just kick it away from your goal."
The seven-time reigning champions nevertheless remain unbeaten this season having dropped points just twice before against Genoa and Atalanta.
Napoli power back
Earlier Arkadiusz Milik and Lorenzo Insigne scored quick-fire goals and Simone Verdi added a third from the spot as Napoli got back on track.
AC Milan had dented Carlo Ancelotti's side's title hopes with a goalless draw in the San Siro last weekend before dumping the southerners out of the Coppa Italia midweek.
"Napoli are back strong," said Ancelotti.
"Today we found the depth and the ability to quickly overturn the game.
"The two tests against Milan were not our usual selves, we're back to our normal standard."
Sampdoria striker Fabio Quagliarella was thwarted in his bid to set a new record of scoring in 12 consecutive Serie A games as the side from Genoa also missed the chance to move up into fourth and the Champions League places.
But Quagliarella " who is from Naples and had scored in Sampdoria's 3-0 win over Napoli earlier in the campaign " was denied his best chance to make history by a sliding Kalidou Koulibaly tackle.
Napoli skipper Marek Hamsik " reportedly set for a move to China " returned from injury and orchestrated the opener after 25 minutes in the San Paolo Stadium.
The Slovak international's cross found Jose Callejon who burst through to provide the assist which Milik finished off for his 12th league goal this season.
Less than a minute later Insigne connected sweetly with another Callejon assist for his first league goal in three months.
Napoli were awarded a penalty for a Joachim Andersen handball but despite the calls of "Kalidou, Kalidou" from the crowd for the Senegalese defender to take it after his towering performance, it was Verdi who stepped up to convert in the final minute.
Sampdoria remain sixth, two points off AC Milan in the final Champions League berth.