Champions Juventus were left stunned by a 15-minute Giuseppe Rossi hat trick as Fiorentina stormed back from a 2-0 half-time deficit to claim a dramatic 4-2 win at a rocking Stadio Artemio Franchi.
Juventus appeared to be coasting to a fifth consecutive Serie A success when Carlos Tevez and Paul Pogba netted shortly before the interval.
However, the game was turned on its head in a stunning burst after Rossi netted a 66th-minute penalty.
The Italy international then levelled on 76 minutes before a totally unmarked Joaquin fired the hosts ahead moments later.
Rossi then completed his hat-trick, and a barely believable win, when he finished a counter-attack on 81 minutes.
Unsurprisingly the 26-year-old left the pitch to wholehearted applause when coach Vicenzo Montella opted to retire him to the bench moments later.
Defeat was Juve's first in the league since February and their first in Florence for 15 years.
There was no sign of what was to come, though, when Juve scored twice in three minutes at the end of the first half.
Tevez won and converted a debatable 37th-minute penalty after contact with Gonzalo Rodriguez, before Pogba headed into an empty net after Juan Guillermo Cuadrado scooped an awkward-looking diving clearance into the Frenchman's path.
But after Antonio Conte's side controlled the first half, the defensive ills which marked their Champions League home draw with Galatasaray before the international break were cruelly exposed.
Kwadwo Asamoah started the rot when he was caught on the wrong side of Matias Fernandez and a tangle of legs brought the Fiorentina man down.
Rossi fired the spot-kick just out of Gianluigi Buffon's reach.
The leveller was not far away and there was little Buffon could do about it as Rossi expertly picked his spot with a well-hit shot across him from the edge of the area.
Juve were now suddenly rocking and there was not a defender in sight when Borja Valero slid a pass to Joaquin, who had more than enough time to take a touch and score from 12 yards.
Rossi then confirmed the win when he curled in his hat-trick after Cuadrado broke and fed him the ball at the top of the area.