Portugal legend Ronaldo then set up Gonzalo Higuain to put Juve 3-0 up.
And moments later he got his 56th career hat-trick when he slipped the ball under goalkeeper Robin Olsen.
The 34-year-old is in his best scoring run since his £99.2m move from Real Madrid in 2018, scoring in each of his past five Serie A games.
It was Ronaldo’s second hat-trick for Juve, having scored three against Atletico Madrid in last season’s Champions League last-16 tie. He has scored three hat-tricks for Portugal since then.
The former Manchester United forward is the first player since Alexis Sanchez to score a hat-trick in the Premier League, La Liga and Serie A.