Napoli's remarkable 11-game winning streak and perfect start to the Serie A season were brought to a screeching halt on Wednesday when Edin Dzeko's second-half strike sealed Inter Milan's 1-0 triumph.
Napoli are still top of the table with 41 points after 16 games but their advantage over second-placed AC Milan, who beat Salernitana 2-1, narrowed to five points.
Arkadiusz Milik's stoppage-time free kick earned Juventus a 1-0 win at Cremonese on Wednesday, their seventh in a row without conceding a goal.
Cremonese had two goals disallowed in the first half and competed with Massimiliano Allegri's side for most of the game.
"We knew this was going to be a tricky match because Cremonese run hard and harry you constantly. They're well drilled and very physical too, so the lads deserve credit for this result," Allegri said.
Juve are third in the table with 34 points, one clear of Inter in fourth.
Lecce staged a second-half comeback to beat Lazio 2-1 at home on Wednesday, inflicting a second Serie A defeat in a row on Maurizio Sarri's side.
While Ciro Immobile put the visitors ahead after 14 minutes, Lecce fought back in the second half to leave Lazio outside the top four in Serie A on 30 points.
AC Milan won their first game after the World Cup break with victory at Salernitana as Rafael Leao and Sandro Tonali struck in the first half.
"We knew we had been working well, although some friendlies didn’t go the way we wanted. But it is just a little step we needed to take to move toward bigger goals," Milan coach Stefano Pioli said.
Atalanta extended their winless streak to four with a 2-2 draw at Spezia. Mario Pasalic saved a point for the visitors with a goal two minutes into stoppage time.
Roma midfielder Lorenzo Pellegrini converted a penalty against Bologna in Rome, scoring the only goal in a 1-0 win as coach Jose Mourinho served his first match of a two-game suspension.
Both teams paid tribute at Stadio Olympico to the late Bologna coach and Roma player Sinisa Mihajlovic, who passed away in December after a long battle with cancer.
