Watch as Giacomo Bonaventura rolled back the years with a scorcher, Domenico Berardi converted two fine penalties and Maxime Lopez drilled in the daisy-cutter.
Fiorentina had taken the lead just before half-time with a spectacular Bonaventura screamer that went in off the underside of the crossbar.
Gaetano Castrovilli was unlucky not to make it 2-0 when his curler came off the far post.
However, Berardi was introduced at half-time and transformed Sassuolo completely, converting two unstoppable spot-kicks in three minutes.
Lopez completed the turnaround with his second Serie A goal, a precise finish from the edge of the area.