Ronaldo found the net in the 38th and 42nd minutes to lift Juve from eighth place, putting them a point behind leaders Milan, who have a game in hand.
The Portuguese draws level with Milan’s Zlatan Ibrahimovic on eight goals at the top of the Serie A scorers’ list.
Milan travel to fourth-placed Napoli on Sunday.
Juve have played a game more than all of the rest of the top five, so their occupation of second may only be temporary.
With four wins and four draws, they remain unbeaten in the league this season, alongside Milan and third-placed Sassuolo.
That includes a 3-0 over Napoli, a result that was awarded when Napoli failed to fulfil a fixture in October.