Knowing a win would restore their eight-point cushion over Lazio, the Old Lady were undone by a brace from Mauro Icardi. Sebastian Giovinco's early penalty had put them ahead, and when Gaetano Berardi was sent off, it looked to be a stroll for Juve, but Icardi had other ideas.
Napoli are third, seven points behind, after a 4-1 drubbing of Roma in Sunday's evening kick-off. Edinson Cavani was the star of the show, displaying why he is one of the most sought-after players on the planet, scoring a brilliant hat-trick to see off the 10-man capital club.
Cavani scored either side of half-time and soon made it eight from 11 appearances against Roma. Pablo Osvaldo did pull one back, but Miralem Pjanic was then sent off and Christian Maggio added a fourth.
Juventus were not the only side to miss a trick on Sunday as Fiorentina, sitting in fourth, lost 2-0 at home to struggling Pescara. Mattia Perin kept La Viola at bay throughout a one-sided first-half, but in the second period goals from Jonathas and Mervan Celik turned things around.
Inter Milan also found their luck had run out as they were humbled 3-0 at Udinese, with their performance a far cry from the form they had displayed in the months leading up to Christmas. Antonio Di Natale was on target twice with Luis Muriel also scoring for Francesco Guidolin's side, who were aided by a red card for Juan Jesus in the 65th minute.
AC Milan were able to take advantage of the slow movers above them, closing the gap on the top six thanks to a 2-1 win over Siena. Second-half goals from Bojan Krkic and Giampaolo Pazzini earned the Rossoneri the points with Michele Paolucci scoring a late consolation for the Tuscans, who remain rooted to the foot of the table, six points adrift of safety.
Elsewhere, Isaac Cofie's first goal for Chievo settled a narrow 1-0 victory over Atalanta that keeps the Gialloblu in the hunt for a top-half finish, and Marco Borriello struck a second-half brace to help Genoa down fellow strugglers Bologna 2-0 and claim only their fourth league win of the season.
In the day's other game, a last-gasp goal from substitute Amauri condemned his former club Palermo to another defeat at Parma, the home side winning 2-1.