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.
