Reigning Serie A champions Juventus were reduced to 10 men and soundly beaten by Cesare Prandelli’s Fiorentina who move up to 14th.
Meanwhile, the defeat dents the Old Lady’s Scudetto hopes, as they sit seven points behind leaders AC Milan, down in fourth spot, with both Inter Milan and Napoli ahead of them.
“We entered with the wrong attitude and when you go on the pitch like this, you go against bad figures, then there we were down to 10 men, and at that point, it was difficult to recover,” Pirlo said.
“Sometimes it happens that we are not 100%, but in the second half we entered with the right mentality.
“It could have been better. Now we have to start again with desire, thinking about the mistakes we made and carrying out our project.”
La Viola scored early on the break with Franck Ribery released Duan Vlahovic to chip over Wojciech Szczesny in the third minute, before Juan Cuadrado received his marching orders, with the video assistant review upgrading a yellow card upon review.
Aaron Ramsey was sacrificed as Pirlo was forced into a 20th minute re-shuffle, with the former Arsenal man’s frustration boiling over on the sidelines as he kicked water bottles.
Fiorentina added a second in the 76th minute when Alex Sandro put the ball in his own net before Martin Caceres made it 3-0 five minutes later.
On Wednesday, leaders Milan host eighth-placed Lazio in the pick of the action.