Torino missed from the penalty spot for the third time this season, and were made to pay the price as Sassuolo scored a late winner to take all three points.
Giampiero Ventura surprisingly chose to field just one striker, Fabio Quagliarella, with midfielders Juan Sanchez Mino and Omar El Kaddouri given license to support the former Napoli man.
Omar El Kaddouri had Toro's first effort on goal, but his curling effort was well saved by Andrea Consigli. Torino had the chance to take the lead after good work from Bruno Peres led to Paulo Cannavaro bringing down Fabio Quagliarella in the area.
Juan Sanchez Mino became the fourth different Granata player to take a penalty this season, but his weak effort was well saved by Consigli. In the second half, Peres broke clear of the Sassuolo defence but his pass across goal to find Quagliarella was intercepted.
Sassuolo's best chance of the game arrived when Simone Zaza somehow managed to blaze over the bar from ten yards out following Nikola Maksimovic's goal line clearance. Excellent work from Omar El Kaddouri gave Quagliarella another chance to give Toro the lead, but he was once again denied by the excellent Consigli.
With just three minutes remaining, Toro switched off from a corner and that allowed Antonio Floro Flores to head home Šime Vrsaljko's excellent cross.
This was a disappointing result for Torino ahead of an important week, and their failure to rectify their terrible record from the penalty spot exemplifies the problems the Granata have been having this season.