The Serie A champions rarely troubled keeper Marco Sportiello on what was proving to be a frustrating night for the team and their £99m signing.

But in the 81st minute, the Portuguese forward finally found the net with a firm strike from eight yards.

And in stoppage time, Federico Bernardeschi fired in the second goal.

Even though the visitors had 72% of possession, the scoreline somewhat flattered the Serie A giants, who only managed eight shots on target from 30 efforts.

Ronaldo had looked the most likely to score in the first half, testing Sportiello's reflexes with two angled drives.

Alex Sandro's second-half strike from inside the area, which whistled a foot past the Frosinone post, was the only other effort of note aside from the two goals.

The win moves Juventus three points clear of second-placed Napoli in Serie A. Frosinone, promoted from Serie B in May, remain in 19th spot with one point from five games.