Carlo Ancelotti’s side took advantage of third-placed Inter’s defeat at Juventus on Friday by extending their lead over the Nerazzurri, although they are eight points off the pace set by the champions.
The Napoli coach picked a heavily rotated side with one eye on their crucial Champions League game at Liverpool on Tuesday, but Piotr Zielinski and Adam Ounas struck before the break and a second half Milik brace sealed a comfortable win.
Napoli needed just seven minutes to take the lead as Zielinski fired a shot into the bottom corner after a period of pressure from the home side.
Shortly before the interval they doubled their advantage in style when Ounas struck a powerful shot into the top corner from almost 30 metres.
The Polish striker took his seasonal tally to seven league goals, already a record for him in a single Serie A season, while Faouzi Ghoulam marked his return after more than a year out injured with two assists.
Napoli have 35 points from 15 games, while Frosinone remain second-bottom on eight points. (Editing by Ken Ferris)
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