Juve were given an unexpected boost in the title race earlier on Sunday when Inter were held 1-1 at Lecce, and Ronaldo ensured his side took full advantage.
Maurizio Sarri's men were not wholly convincing but, in the Portuguese, had the game's outstanding player, who opened the scoring late in the first half.
Andreas Cornelius outjumped Ronaldo for an unlikely equaliser, yet revenge was swift for the five-time Ballon d'Or winner, a second goal soon sealing victory for the leaders.
Alex Sandro headed just over from an early corner, but the left-back had to be replaced by Danilo after 21 minutes as Juve struggled to get into their stride.
Ronaldo worked room for a shot on the right-hand side of the area, drawing a good save from Luigi Sepe that prompted another corner from which the Juve number seven wastefully missed the target.
The former Real Madrid superstar continued to provide the Bianconeri's chief threat and forged the breakthrough two minutes before half-time, cutting inside from the left to shoot hard and low, his effort taking a deflection that wrongfooted Sepe and nestled in the net.
Aaron Ramsey drilled agonisingly wide before the break, while only a superb one-handed Sepe stop denied Danilo from 20 yards following the restart.
It was a Parma substitute who scored the next goal, however, Cornelius - on for Roberto Inglese moments after the opener - rising above Ronaldo from a right-wing corner to nod in a towering header.
But Ronaldo's response was ruthless, meeting Paulo Dybala's cutback with a clinical first-time finish just three minutes later to clinch the points.
He might have completed his hat-trick in the closing minutes, but Sepe blocked a strike from the right before a header from the consequent corner looped over, and a curled strike from the left drifted wide.
Ronaldo reigns
The talismanic forward was signed largely to lead a Champions League charge, but Inter's impressive form has meant Juventus must also rely on Ronaldo to do the business domestically. He made no mistake on Sunday, deserving his fortune for the first goal and tucking away the second in style.
