Dejan Kulusevski and Alvaro Morata were also on target although it could have been very different if Juve’s 42-year-old goalkeeper Gianluigi Buffon had not saved with his legs at close range from Juraj Kucka in the 15th minute.
Juventus, chasing a 10th successive title. Ronaldo’s brace made the irrepressible Portuguese the league’s topscorer, the 35-year-old moving two goals clear of AC Milan’s Zlatan Ibrahimovic and Inter Milan’s Romelu Lukaku as he bounced back from his penalty miss against Atalanta on Wednesday.
Juve, however, quickly took control and Kulusevski, who played for Parma last season, was given too much space in the penalty area and steered the ball in.
Ronaldo added the second with a towering header three minutes later and Juve were on their way.
Morata was rewarded for an excellent performance with the fourth as he headed in from Federico Bernardeschi’s cross late in the game.