Gianluigi Buffon was sent off and Juventus was held to 1-1 at Lazio on Saturday, ending the two-time defending champion's 12-match winning streak in Serie A.
It was the second disappointment this week for Juventus at the capital's Stadio Olimpico, after being eliminated from the Italian Cup with a 1-0 loss to Roma on Tuesday.
Still, Juventus holds a nine-point lead over Roma, which visits Hellas Verona on Sunday.
Buffon was shown a red card for taking down Lazio centre forward Miroslav Klose in the 24th minute and Antonio Candreva converted the ensuing penalty kick.
Fernando Llorente equalized for Juventus in the 60th with a header following a cross from Stephan Lichtsteiner.
Marco Storari, who replaced Buffon in Juve's goal, tipped a header from Klose off the crossbar in the 75th.
Storari was also fortunate when Lazio teenage forward Keita Balde hit the post in the 86th with the goalkeeper beat.
Earlier, Napoli was held to 1-1 at home by Chievo Verona and remained third, 12 points back.
At Naples' San Paolo stadium, Chievo defender Gennaro Sardo put the visitors in front in the 18th after being set up by Cyril Thereau.
Napoli defender Raul Albiol equalized in the 88th with an acrobatic effort.
"It's not easy to play against squads that close down so much but clearly we need to rediscover the intensity and velocity that we had at the start of the season," Napoli manager Rafa Benitez said.
On Sunday, struggling AC Milan plays at Cagliari and fourth-place Fiorentina hosts Genoa in the late match.