The second half started equally slow, and Real Madrid didn't take a shot until Ronaldo doubled their lead in the 73rd minute.
Ronaldo bagged a hat-trick, a record equalling seventh in the competition, as Madrid thrashed their cross-city rival Atletico Madrid 3-0 in the semi-final first leg.
The Portugal forward headed Real in front on 10 minutes, although he appeared to have been offside in the initial build-up.
"Cristiano is a goalscorer".
"You can play well in defence, you can control the middle but you need a player who can score to get the result. I'm pleased with all of my players". We are going to try until the very, very end, until the final whistle is blown in the second leg. We know exactly how we have to play. We then had width with (substitutes) (Lucas) Vazquez and (Marco) Asensio.
"We know the importance of this first game and it's all we are thinking about", Madrid coach Zinedine Zidane said on Monday. "We can hurt any side with our weapons", said Real Madrid boss Zinadine Zidane. "We interpreted the game very well". "The team was phenomenal and to score three goals made it a special night", he added.
Karim Benzema felt Real Madrid left little doubt over their supremacy in the Spanish capital with a dominant 3-0 Champions League semi-final triumph over neighbours Atletico.
Zidane, though, warned against any complacency. "We must remain cool and look to win in the second leg too". We will have to work hard and fight for it.
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Nacho Fernandez replaced Dani Carvajal in the Madrid side after the break after the right back suffered a muscle injury in the last action of the first half.
"We need to forget about this game", said the Argentine.
"I'm really happy for that".
"I don't think that we are euphoric and imagining ourselves in the final".
Atletico saw more of the ball but failed to create chances against a solid Real defense and Diego Simeone reacted by bringing Nico Gaitan and Fernnado Torres on for Gameiro and Saul, while Zidane replaced Isco.
"It's great to have a player like Ronaldo", he said.
First Goal: Cristiano Ronaldo from the centre of the box to the centre of the goal.
"It's very complicated, but it's football". "It seems impossible, but it is football and football has these unexpected things that make it marvellous". We have to go into the return leg at the Calderon fully focused.