(CNN) -- Juventus were left searching for answers after their unbeaten run was shattered by Fiorentina.
The home side staged a renaissance in Florence that the city's medieval residents would have been proud of as they turned a 2-0 half time deficit into a 4-2 triumph.
It was the first loss of the season for Italy's Serie A champions, Juventus.
"We lost a game that we dominated for 70 minutes," Juve manager Antonio Conte said on the club's website.
"We were home and dry and had more than one opportunity to score the third goal.
"Suddenly something strange happened, if I could explain why it would be simple."
Juventus defender Andrea Barzagli was equally baffled: "I honestly don't know how to explain what just happened.
"We dominated the game, going close to scoring a third goal, and before we know it we find ourselves 3-2 down. There weren't even signs of a potential Fiorentina comeback."
A first half penalty for Carlos Tevez, who had been brought down by fellow Argentine Gonzalo Rodriguez, and a Paul Pogba strike had given Juventus the lead.
Fiorentina's revival began in the 66th minute when Giuseppe Rossi slotted in a penalty.
The American born striker found the back of the net 10 minutes later as he drove the ball beyond Juventus keeper Gianluigi Buffon.
Joaquin caught the away side on the break to add a third for Fiorentina before Rossi wrapped up his hat trick in a stunning 14-minute spell.
Fiorentina coach Vincenzo Montella said: "This is the best result ever. It's difficult to score against Juve so putting four past them gives us immense satisfaction."
The result saw Juventus drop to third in the table behind Roma and Napoli while Fiorentina are sixth behind Inter Milan.
The Milan side were held to a 3-3 draw by Torino in a dramatic match which saw goalkeeper Samir Handanovic sent off after just six minutes.
Handanovic was shown the red card after he was judged to have brought down Torino striker Alessio Cerci.
Inter were playing their first match since Indonesian tycoon Erick Thohir bought a 70% share in the club.
A win looked to be on the cards only for Torino's Nicola Bellomo to curl a free kick into the net in the dying moments of the match.
Monaco held by Sochaux
In France, Monaco also threw away a 2-0 lead to settle for a 2-2 draw away at Sochaux.
Belgian Yannick Ferreira Carrasco had fired the Principality side into the lead inside the opening 10 minutes.
But Sochaux refused to give up and second half goals from Cedric Bakambu and Joseph Loppy rescued a share of the points.
"I spoke a lot this week about the psychological aspect and after ten minutes I was thinking that was all for nothing," said Sochaux manager Herve Renard.
"But in football you should never give up, and it was a great reaction."
Monaco coach Claudio Ranieri said his side "left our concentration in the dressing room" at the break.
The result saw Monaco fall two points behind league leaders Paris Saint-Germain.
The French champions had beaten Bastia 4-0 Saturday, a result that included a dazzling back heel from Zlatan Ibrahimovic that has been dubbed a "scorpion" strike.