- Abdou Harroui (7' Pen)
- Matteo Politano (24')
- Victor Osimhen (42', 79')
Napoli now have Rudi Garcia in the dugout after Luciano Spalletti took the Italy national team job and the Naples side had a horror start when they conceded a penalty inside five minutes.
Jens Cajuste tripped Jaime Báez when attempting to clear the ball and Abdou Harroui stepped up to convert the spot kick to give Frosinone -- who won the second-division Serie B title last season -- a 1-0 lead against the champions.
Napoli were shell-shocked but they quickly recovered and equalised in the 24th minute when Matteo Politano pulled the trigger from the edge of the box to beat the keeper.
Giacomo Raspadori thought he had made it 2-1 for Napoli after an acrobatic assist from Osimhen, who threw himself into the air near the post to set up the shot with his foot, but the goal was chalked off for offside in the build-up.
However, Osimhen ensured they went in ahead at the break when last season's top scorer received the ball after a run from Giovanni Di Lorenzo and unleashed a piledriver from an angle that grazed the underside of the crossbar on its way in.
Baez nearly equalised for Frosinone after the restart when he sent a free kick sailing towards goal, but the Uruguayan's shot cannoned off the post to give Napoli a reprieve.
But Osimhen made it 3-1 to Napoli when he broke the offside trap in the 79th minute and, with just the goalkeeper to beat, the Nigerian striker fired a low shot to find the back of the net as Garcia's side sealed all three points.
- Matteo Marcenaro