Inter Milan maintained a two-point lead at the top of Serie A on Sunday after running out convincing 3-0 winners at Napoli, whose title defence already appears on its last legs.

Beautifully taken goals from Hakan Calhanoglu, Nicolo Barella and Marcus Thuram pushed Inter back above closest challengers Juventus, who briefly held top spot after beating Monza on Friday.

Sunday's thumping was a show of force from Inter who illustrated why they are favourites to win a 20th league title, last season's losing Champions League finalists looking set for another memorable season.

Napoli are now 11 points off the pace and travel to Juve next weekend in a match which could end any realistic hope of the champions retaining the Scudetto before the calendar year is out.

To add insult to injury Napoli have dropped out of the top four, replaced by Roma who won 2-1 at Sassuolo earlier and took fourth spot on goal difference.

Simone Inzaghi's side have won 11 of their 14 league matches so far this season and once Hakan Calhanoglu thrashed in the opener on the stroke of half-time they expertly dealt with a hyped-up Napoli.

Hosts Napoli were playing their first home fixture under returning coach Walter Mazzarri, whose team are stuck on a paltry seven points from as many matches at the Stadio Diego Armando Maradona.

Barella doubled Inter's lead just after the hour mark with his first goal of the season, shortly after Yann Sommer pulled off a brilliant save to deny Khvicha Kvaratskhelia, one of three superb stops from the Swiss.

Italy's Barella burst unopposed from midfield and after collecting Lautaro Martinez's low pass skipped past Leo Ostigard and Natan before confidently finshing past Alex Meret.

And with five minutes remaining Thuram made absolutely sure of the points, tapping home his fifth goal of a brilliant first season at Inter from substitute Juan Cuadrado's low cross.

Paulo Dybala's 76th-minute penalty and a wildly deflected strike from Rasmus Kristensen shortly afterwards earned Roma a win from their scrappy match with Sassuolo, who finished with 10 men after Daniel Boloca was sent off in the 63rd minute.

The draw at the Mapei Stadium came as coach Jose Mourinho is reportedly being investigated by the Italian Football Federation (FIGC) for saying that referee Matteo Marcenaro didn't "have the emotional stability to referee at this level" ahead of the match.

The Portuguese blasted Marcenaro, 31, in a pre-match outburst on Saturday which the country's refereeing association said "could lead to violence" against officials.

However, Mourinho was backed by Roma on Sunday, General Manager Tiago Pinto saying that the coach "didn't insult anyone" and that the club hadn't been informed of any FIGC probe.

And despite having excellent Italian he insisted on only speaking in Portuguese in his post-match interview with DAZN, thanking Roma through an interpreter for the support.

"I am speaking Portuguese because my Italian is not good enough to explain certain concepts," said Mourinho.

"When I spoke about emotional stability, I was talking about a quality that is necessary in both life and football in order to perform at the highest level."

Fiorentina are a point behind Roma and Napoli in sixth thanks to a simple 3-0 win over the division's bottom team Salernitana.

Meanwhile Bologna are a further point and place back after Roberto Piccoli's penalty in the 10th minute of added time cost Thiago Motta's team a 1-1 draw at Lecce.