Inter Milan ended Juventus' 49-match unbeaten streak in Serie A with a 3-1 comeback win over its bitter rival in "Italy's derby" on Saturday and moved within one point of the lead.
For its ninth consecutive victory in all competitions, Inter also had to overcome questionable refereeing.
Chile midfielder Arturo Vidal put Juventus ahead after just 18 seconds, but replays clearly showed that Kwadwo Asamoah provided the cross while offside.
In the 12th minute, a goal from Inter forward Rodrigo Palacio was annulled for another questionable offside call, this time with replays indecisive.
However, Inter eventually equalized with a penalty from Diego Milito in the 59th after Claudio Marchisio tugged the Argentine's jersey. Milito scored the winner by firing in a rebound in the 75th.
As Juve pressed forward for an equalizer, Palacio scored Inter's third in the 90th, finishing off a counterattack with a pass from Japan fullback Yuto Nagatomo.
Juventus had not lost in the Italian league since being beaten by Parma 1-0 the penultimate match of the 2010-11 season. The Bianconeri was unbeaten last season en route to the title.
AC Milan holds the record unbeaten streak at 58 matches, set from 1991 to 1993.
"The first goal was offside, but after that goal we reacted well and had a great match," Milito said. "We had a lot of courage to play like this in this stadium. Nobody had ever done that before."
Juventus Stadium opened last season and this marked the Bianconeri's first loss there.
Juventus midfielder Stephan Lichtsteiner was fortunate not to be shown a second yellow card, and was substituted for before halftime.
"We're following our own road," Milito said. "We've still got an extraordinary squad ahead of us and I'm sure they won't give up until the end. We've just got to try and keep winning and then we'll see what happens at the end."
Earlier, Milan moved into the top half of the table with a 5-1 rout of Chievo Verona, boosting manager Massimiliano Allegri's chances of holding onto his job.
Urby Emanuelsson opened the scoring for Milan in the 16th minute at the San Siro and while Sergio Pellissier equalized for Chievo two minutes later, the Rossoneri got two more goals from Riccardo Montolivo and Bojan Krkic before halftime.
Stephen El Shaarawy added another in the 75th for his league-leading eighth goal of the season, and Giampaolo Pazzini found the target in added time.
Milan moved into a tie for seventh place with Roma and Cagliari, 14 points behind Juventus.
"I think Milan is back," club vice-president Adriano Galliani said. "I just spoke with the president (Silvio Berlusconi) and we both said the same thing, 'We seemed like Milan tonight.' He really liked Bojan and he told me to compliment the coach.
"We're a bit calmer now with the seven points from the last three matches, which have given us a bit of a jump. We've got a squad that can't not finish in the top places."
Milan lost five of its opening eight matches and Allegri has been fending off speculation that he could be fired for several weeks. This week, Milan needed two late goals to rally for a 2-2 draw at Palermo.
"Any other club in our situation would have changed coaches," Galliani said. "I've got a great relationship with Allegri."
Emanuelsson's opener came with a deflected shot from the edge of the area and Montolivo's and Bojan's goals were also deflected.
Pellissier's goal came with a header following a corner kick.
El Shaarawy, who turned 20 a week ago, scored from close range, redirecting a cross from Ignazio Abate, then provided the cross for Pazzini's goal.
"El Shaarawy is more than a prodigy now," Galliani said. "He's a little champion."
Chievo defender Boukary Drame was hit in the face by the ball and carried off on a stretcher, but coach Eugenio Corinin said medical tests showed no major injuries.