Maurizio Sarri's team had briefly been deposed by title rival Juve after the reigning Serie A champion ran riot to beat Sassuolo 7-0 in Turin earlier in the day.

Goals in the first and second half from Mertens and Marek Hamsik respectively secured a comfortable victory for the visitor at Stadio Ciro Vigorito.

Mertens opened the scoring in the 20th minute when he benefited from some clever play by Allan before directing a cross to the back post which, perhaps accidentally, fooled Benevento goalkeeper Christian Puggioni and fell over the line.

Just two minutes into the second half, Gaetano Letizia gave away possession in a dangerous area and Napoli pounced, Hamsik arriving at the back post to meet Jose Callejon's pass across the face of goal and steer home a simple finish.

Benevento was denied a penalty in the 56th minute when Kalidou Koulibaly committed a clumsy foul, only for the video assistant referee (VAR) system to show a Benevento player had been in an offside position during the build-up to the incident.

Mertens was withdrawn with 16 minutes to go after receiving a kick to the heel, and Sarri will hope the Belgian is not seriously hurt as attention turns to the visit of Lazio to Stadio San Paolo next weekend.