Despite leading through Sami Khedira's early strike, Mariusz Stepinski's first-half header and Emanuele Giaccherini's penalty after the break ensured Chievo led.
Mattia Bani's own goal levelled matters with 15 minutes to go and Mario Mandzukic thought he had won the game for Juventus only for VAR to disallow the goal, with Ronaldo having possibly handled and collided with goalkeeper Stefano Sorrentino in the build-up.
Yet Bernardeschi turned home Alex Sandro's cross in the 93rd minute to give Ronaldo and Juve a winning start.
Three minute into Ronaldo's bow Juve were 1-0 up, though it was another former Real Madrid man that got the goal.
Miralem Pjanic's free-kick was reached by Giorgio Chiellini at the back post and his header was latched on by Khedira, who swivelled and fired home a half volley.
Ronaldo missed the target with two openings and Chievo struck back prior to the break when Stepinski peeled off Leonardo Bonucci and headed in an equaliser.
Juve then fell behind when one of their former players converted a 56th-minute penalty. Joao Cancelo, another Juve debutant, dived in on Giaccherini to concede the penalty and the midfielder took the spot-kick himself to put Chievo ahead.
Trailing in the game seemed to galvanise Ronaldo and, after heading straight at Sorrentino, he unleashed a terrific effort from range that the Chievo keeper had to palm away.
Only a brilliant last-ditch intervention from Fabrizio Cacciatore then denied Ronaldo, but his side did level when Bani put into his own net when trying to deal with Juve's returning defender Bonucci at a neat-post corner.
A dramatic finish then unfolded as Juve were denied a Mandzukic goal that was initially awarded. Replays showed the ball struck the back of Ronaldo's arm before he collided with Sorrentino, who was laid out when the ball looped up for Mandzukic to head home.
But Juve did net a winner as Bernardeschi scored past substitute goalkeeper Andrea Seculin, much to Ronaldo's delight.
What does it mean: Ronaldo not up and running, but Juve show champions' mentality
Ronaldo had scored in each of his last 10 league appearances for Madrid, but that was not a sequence that was extended to Serie A. Dropping deep at times and showing frustrating at not receiving the ball on other occasions, it will take time for the 33-year-old to find his place in this Juve team. The most pleasing thing from the Bianconeri's point of view was that others stepped up and they found a way to win.
Pat on the back: Bernardeschi steals the limelight
Bernardeschi was called for immediately after Juve fell behind and having provided the corner from which they levelled, the winger was then in the right place at the right time to score the winner. In delivering when it mattered, he took a leaf straight out of Ronaldo's book.
Boot up the backside: Cancelo's debut to forget
Another of Juventus' new signings Cancelo will not remember his first appearance too fondly. The first goal Juve conceded came via a cross from his flank and he then dived in needlessly to concede the penalty which saw Chievo go 2-1 up.
