Gervinho matches Ronaldo double as Parma frustrate Juventus
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 their 3-0 defeat to Atalanta ended their four-year Coppa Italia reign.
But it was not the response Allegri had called for ahead of their Champions League last 16 first leg tie against Atletico Madrid on February 20.
Juve, 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 margin on Napoli with Inter Milan 20 points behind in third.
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 scoring for the hosts on 62 mintues.
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.