The visitors just about deserved the three points for the way they had dominated exchanges until the dismissal of Ronaldo on 68 minutes for deliberate handball and a second yellow card.
"Today the focus was very good," Reds boss Sir Alex Ferguson told Sky Sports News.
"Last week our game dropped against Aston Villa and I think that was down to focus and our focus was great today."
"We have had a significant result today and I hope it makes a difference."
When asked about Ronaldo's dismissal, the United chief said: "I have seen it again and I think he was trying to protect his face.
"He may have got a little shove. He thought he had heard a whistle but I am not going to talk about the referee. We could be here all day."