Ronaldo scored the winner in the 2-1 win over 10-man Manchester United - his first return to Old Trafford since he left the club in 2009 - to put Real Madrid into the quarter-finals 3-2 on aggregate.
Afterwards he told Sky Sports: "It was emotional in both games, especially tonight, it was unbelievable."
He added: "I don't have words to explain what I feel. I just have one word to say it is unbelievable.
"What the supporters did made me feel quite shy because in my opinion in both games I didn't play like I play all the time.
"But anyway I helped my team to score one goal home and away. I feel happy inside because Madrid got through but on the other hand I feel a little bit sad because Manchester United deserved (to win).
"But it's part of the football. It's feelings that stay in there and this doesn't change things."
The match swung on a red card shown to Nani while United were 1-0 up - a decision which incensed the home side.
Ronaldo added: "To be honest I didn't see the replay of what Nani did but these situations happen in football. I'm not going to say any more because I didn't see the replay."
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