Arkadiusz Milik has given Napoli the half-time lead in their Coppa Italia clash, but Sassuolo saw an equaliser disallowed via VAR.
The winners will go on to face Milan in the quarter-final later this month.
The Partenopei had to do without Dries Mertens, Marek Hamsik, Raul Albiol, Piotr Zielinski and suspended Simone Verdi, while Sassuolo missed Marlon, Gian Marco Ferrari, Federico Di Francesco, Claud Adjapong and Alessandro Matri, but Kevin-Prince Boateng returned from a long lay-off.
Only four Neroverdi fans made the trip down to the Stadio San Paolo, with the overall attendance at around 15,000.
It was a bright start from both sides, as Domenico Berardi failed to make the most of a defensive error and on the counter Jose Callejon fired straight at the goalkeeper one-on-one.
The opening goal came at the end of a long period of Napoli possession, as Gianluca Pegolo flapped at Lorenzo Insigne’s cross and it ricocheted in off the stomach of Arkadiusz Milik.
The hosts continued to dominate the ball and Insigne’s snapshot whistled off target, but Sassuolo thought they had drawn level on 35 minutes with Manuel Locatelli. His initial ferocious strike from distance stung David Ospina’s gloves, the Elseid Hysaj clearance was poor and Berardi sent Locatelli back in to finish it off. However, the referee decided after a VAR review that Locatelli handled in the build-up and the goal was disallowed.
Napoli 1-0 Sassuolo (Half-Time)
Milik 15 (N)
Napoli: Ospina; Hysaj, Maksimovic, Koulibaly, Mario Rui; Callejon, Diawara, Fabian Ruiz, Ounas; Milik, Insigne
Sassuolo: Pegolo; Lirola, Magnani, Peluso, Rogerio; Locatelli, Sensi, Duncan; Berardi, Boateng, Djuricic
See the latest Serie A predictions and betting tips with Eurotips.co.uk