Goals from Arturo Vidal (12’) and Nicola Barella (52’) earned Inter Milan an important three points as they drew level on points with leaders AC Milan who play Cagliari on Monday.
The result leaves Juventus, chasing their 10th consecutive Scudetto, down in fifth spot and seven points off the pace.
“Our attitude was all wrong from the very beginning and when you lack anger and determination in matches like these, its an uphill struggle,” rookie Juventus boss Andrea Pirlo said.
“We dropped deep and were too fearful of Inters attack we were entirely preoccupied by our defensive work, without even being aggressive, but in these sorts of contests you need to match your opponents for competitive desire.
“Over a long run, these slip-ups can happen and its a shame because we came into this in good form, however a team like Juventus can never show that kind of attitude.”
The pressure is starting to ramp up on former Italy international Pirlo who took over in Turin in July, but it could be eased with some silverware when Juve takes on Napoli in the Super Cup in midweek.
“However, if the team fails to do what we rehearsed, its my responsibility,” Pirlo said.
“We couldn’t have put in a worse performance than this but now we need to pick ourselves up because we’ve got a cup final on Wednesday.
While Pirlo was bemoaning his side, opposition boss Antonio Conte was boasting about Inter’s “perfect” display.
“To win against a team like Juve, who in Italy are an important yardstick, you have to get close to perfection,” Conte told Sky Sport Italia.
“Tonight we played a great match and the biggest satisfaction is that we saw some ways we could hurt Juve and, sure enough, they proved to be spot on.”