Juventus' indifferent start to the season continued on Sunday night after they went down 2-0 against fellow title rivals Inter Milan at the San Siro.
Antonio Conte's side scored a goal in each half to claim the win, which moved them level on 40 points with leaders AC Milan, who will be in action on Monday night.
The hosts were more organised in the opening period, and despite the visitors enjoying a larger share of the possession, Inter created more chances during the period.
Juventus thought they had taken the lead in the 11th minute, but Cristiano Ronaldo's goal was ruled out for offside.
Inter then immediately scored their opener as Nicolo Barella swung a ball deep into the box and found Arturo Vidal unmarked, and his close-range header flew past the keeper into the left side of the goal.
The hosts then got a near-perfect chance to double the score in the 24th minute, but Romelu Lukaku's effort was easily saved by the keeper.
The Belgian returned once again in the 38th minute, running onto a loose pass inside the box before releasing a tremendous shot towards the right side of the goal. However, Wojciech Szczesny anticipated the shot and made a brilliant save.
That was the only real piece of the action in the remaining bit of the first half as Inter took a well-deserved lead going into the break.
The second half was evenly balanced even though Juventus seemed out of sorts for long periods and could not find a way through the tight Inter Milan defense.
It did not take long for Conte's men to double their score, and it came seven minutes into the second half as Alessandro Bastoni found Nicolo Barella with a wonderful pass, with the latter taking his time before sticking it past the outstretched goalie.
Inter kept on knocking on Juventus' door, but there were no more goals as Pirlo's side suffered a second win in their last five matches.
The loss means they have dropped further in the race for the Serie A title and will have some catching up to do.