It was a forgettable bow for Ronaldo, who was shown a straight red card following an inconspicuous coming together with Valencia defender Jeison Murillo in an off-the-ball incident, the five-time Ballon d'Or victor left in tears after his dismissal.
Ronaldo now faces an anxious wait to see whether he would miss Juventus' match against Manchester United next month.
This post will be updated.
There is risk too for Juventus, who have shelled out the first three-figure sum ever paid for a player in their thirties, and one that represents a very different model to the free-flowing forward that used to terrorise defences left, right and centre.
The 33-year-old directly contributed to half of Real Madrid's Champions League goals between 2009-10 and 2017-18, coming top of the goalscorer charts in each of the last six seasons.
Champions League rules state a red card means an automatic one-game ban and in case of serious offences, "the UEFA Control, Ethics and Disciplinary Body is entitled to augment this punishment, including by extending it to other competitions".
However, it is Ronaldo's goals that have led Real to so much success on the continent in recent times. "In Spanish I can talk but maybe not go into that amount of detail with them that I would need to".
"What I've said before is that whoever we pick will be a wonderful solution and I have nothing else to add to that", he said.
Despite their numerical advantage, Valencia walked away from a packed Mestalla empty-handed following a pair of Miralem Pjanic penalties.
Valencia probed but even when Daniele Rugani collided with Gabriel for a third penalty, Parejo's shot was saved by Wojciech Szczesny.