Vincenzo Montella's side looked on course to build on an impressive 5-2 victory away at Genoa prior to the international break when Borja Valero broke the deadlock against Cagliari, nodding in at the far post after Giuseppe Rossi helped on a Massimo Ambrosini cross.
But Mauricio Pinilla came off the bench to power home a Victor Ibarbo cross with a just minute of normal time to spare as Cagliari claimed a share of the spoils.
Fiorentina's woes were compounded just moments later when David Pizarro was shown a second yellow card for dissent.
Supporters left the Stadio Olimpico's famous Curva Nord stand empty for the start of the match to show their disapproval at the club's dealings in the transfer market.
Genoa were just as ruthless in the day's evening kick-off, securing an emphatic 3-0 win at Sampdoria.
The visitors made sure of the points after 65 minutes thanks to an well-struck Francesco Lodi free-kick, wrapping up a memorable night for Fabio Liverani's side.
In the day's other games, Hellas Verona condemned Sassuolo to the third consecutive defeat of the season with a 2-0 win, while a brace from Paulinho against Catania saw Livorno record their second win on the bounce with a 2-0 victory.
