The Spain defender's dubious record aside, it was a spectacular start to the three-time defending champions title defence, with Gareth Bale, Isco and returnee Mariano all scoring, the latter's tally his first-ever in the Champions League.
The Portuguese forward, making his Champions League debut for Juve, appeared to grab Valencia defender Jeison Murillo's hair as they tangled off the ball midway through the first half and referee Felix Brych consulted his assistant behind the goal before showing the five-time Champions League victor a straight red card.
Ronaldo's European bow in Juventus colours turned into a nightmare against Valencia when he received his marching orders after just 29 minutes.
Juventus face Young Boys in Turin next, on October 2, before back-to-back games against United and Allegri feels his side have put themselves in a strong position.
"It is very disappointing, we nearly lost because of that and we will be without Ronaldo for the next (game)".
Replays showed there was a slight coming together between the two players, but Ronaldo didn't appear to lash out at his rival with his hand or head.
"We were playing very well until Ronaldo's sending off but we continued to play our football despite that blow and deservedly scored two goals", he said. But Wojciech Szczesny parried Parejo's spot kick, which was awarded after Daniele Rugani was adjudged to have elbowed Gabriel Paulista.
Manchester City suffered a surprise 2-1 defeat at home to Olympique Lyonnais.
Bale nearly increased Madrid's lead with a close-range shot that struck the crossbar early in the second half but the Wales forward did make it 2-0 in the 58th with a well-placed low shot after a superb through ball from Luka Modric.
"I thought the performance was very good tonight; the only disappointment was that we didn't score more", said Bale.
Bayern Munich beat Benfica 2-0.