Sassuolo in the first round of Serie A.
Napoli took the lead through captain Marek Hamsik but Antonio Floro Flores levelled before half time for the home side. Then with just minutes remaining Nicola Sansone won it for Sassuolo.
Sarri’s men started the game well and took the lead after just two minutes when Hamsik turned in a rebound from a Gonzalo Higuain effort.
Domenico Berardi then went close to levelling proceedings when his goal bound shot was deflected but it was not long before Sassuolo got back into the game.
A superb ball from Berardi set up Floro Flores, who was born in Naples, and the striker took the ball on his chest before guiding it past the helpless Pepe Reina, equalising on the stroke of half time.
After the restart Sassuolo began to take control of the game and a great save from Reina denied Gregoire Defrel from giving the Neroverdi the lead.
At the other end, a delightful free kick from Dries Mertens drew the best from Andrea Consigli in the Sassuolo goal. Despite star man Berardi being force off with an injury, it was Sassuolo who would claim all three points.
With just six minutes to go, a Diego Falcinelli cross was helped home by substitute Sansone to condemn Sarri to a first defeat in charge of Napoli.
The result was the first time that Sassuolo has beaten Napoli in a top flight fixture and was the perfect way to start the season.
Napoli, however, will hope for better in their next Serie A game at home to Sampdoria.