Ronaldo scored Real Madrid's first-half equaliser after Danny Welbeck had put the visitors ahead in the first leg of the Champions League last-16 tie at the Bernabeu.
Instead of celebrating the former world player of the year opted to acknowledge the Real fans before making an almost apologetic gesture to the Red Devils dug-out.
"I was in Manchester for six years so tonight [Wednesday] was very emotional for me," the Portuguese said.
"I scored a goal but I didn't celebrate out of respect.
"Maybe United are favourites now, maybe not. Anything can happen. Sometimes we are better away than at home so we will see.
"It will be amazing to play at Old Trafford again after four years. It will be another emotional night."
Sir Alex Ferguson revealed Ronaldo went into the United dressing room to speak with his old team-mates.
"I spoke to him. He is sitting in our dressing room, talking to the lads," said the United boss.
"He had six years with us and I am proud of how he flourished.
"I blamed Patrice Evra for not challenging for his goal until I saw the replay and felt a bit stupid.
"His knee is about as high as Evra's head - phenomenal.
"I don't think any other player in the world can do that, certainly not Messi."
Ferguson said he would have accepted the result prior to kick-off.
However, it required a series of outstanding saves from David de Gea to ensure the tie remained deadlocked.
"De Gea was excellent," Ferguson said. "He made three or four top saves.
"He has been improving all season.
"There was one save in the first half which he touched onto the post (from Coentrao) which was superb.
"I am pleased for him. He is an Atletico boy playing here in Madrid, but he has done well."
Welbeck came within inches of nabbing a second after some slack goalkeeping from Diego Lopez.
And Robin van Persie completely mistimed a volley when he had a clear sight of goal, which allowed Xabi Alonso to clear.
Then, in stoppage time, Van Persie had another goalbound shot turned away by Lopez.
"It was possible for them to win 3-1 because they had two big chances when Alonso cleared off the line and Diego made a save," said Mourinho.
"I won't criticise what they did. United did their job well and got the result they wanted.
"They came here not to concede space and goals and they didn't play to win.
"But they know Real Madrid can do it there."
It is widely assumed Mourinho will find himself out of a job should the Spanish giants fail in their quest.
However, the former Chelsea coach insists he is not under pressure.
"I don't feel any pressure," he said.
"I work hard, am very serious and am happy with what I do.
"I have peace of mind and my head is high, but there is no pressure really.
"I have no idea (if his future depends on the second leg) and I am not worried about it."
However, Ferguson feels such an outcome would be very harsh.
"For Jose to be here as long as he has is unusual and a mark of respect for the work he has done," said the United boss.
"I don't know how many coaches they have had - 25? That's more than the years I have been here."
United now face Reading in the FA Cup on Monday, then have a trip to QPR and a home game with Norwich, giving them a relatively straightforward period until the deciding leg at Old Trafford on March 5.
In contrast, Real have two meetings with Barcelona.
"It doesn't matter unless we win," said Ferguson.
"Jose will have troops revved up for it, but so will we and we have a chance."