Knowing a win won 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 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.
Relegation-threatened Palermo had failed to win in seven previous visits to the Stadio Ennio Tardini, mustering only four draws, and they were never ahead, but a refreshed line-up caused Parma plenty of trouble on the counter-attack.
Parma survived their visitors' early enthusiasm to snatch the lead through Ishak Belfodil midway through the second half but Igor Budan pegged his former employers back with an equalising header.
Amauri would have the last word, though.
Lazio cut Serie A leaders Juventus' lead to five points on Saturday night with a 2-1 home win over struggling Cagliari.
It took a late penalty from Alvaro Candreva to decide the outcome, with Cagliari having two men sent off after the spot-kick was awarded.
Goalkeeper Michael Agazzi was dismissed first, receiving his second yellow card of the game for the foul on Miroslav Klose that resulted in the penalty, and for protesting excessively midfielder Andrea Cossu was also ordered off.
Cagliari had gone ahead after 62 minutes when Marco Sau struck, but Abdoulay Konko levelled 10 minutes from the end and in the 86th minute Candreva secured all three points for second-placed Lazio.
Juventus still have a comfortable cushion, and on Sunday can restore their eight-point advantage when they tackle Sampdoria in Turin.
Earlier, Catania and Torino shared a tame goalless draw at the Stadio Massimino in the first Serie A game of 2013.
The Sicilians held on for a point, despite playing nearly the full game with only 10 men following an early red card for Francesco Lodi, who lashed out in retaliation towards Riccardo Meggiorini and receiving his marching orders from referee Mauro Bergonzi.
Catania squandered a penalty when Gonzalo Bergessio sent his kick against the crossbar.
Saturday's Serie A Results
Sunday's Serie A Results