Alexis Sanchez equalised for the visitors, scoring on the rebound after Manuel Neuer saved his 30th-minute penalty, but that seems of little outcome now before the second leg in London on March 7.
No one has been as dominant as Ronaldo in this stage of the European competition.
Stay tuned here for goals and highlights of key plays throughout the match.
He scored once in each game against former club Manchester United the following year, then netted four times against Schalke in 2013-14, and three times against the same German club the following year.
Madrid will likely need Ronaldo to thrive again this time against Napoli, as Bale will not play despite having recovered from right-ankle surgery.
But despite Zidane saying, "We've got all our players back" as he met press to preview the game, he decided not to risk the 27-year-old.
Both sides will probably line up in like for like 4-3-3 formations, so the game may depend on individual brilliance to decide the outcome. Each team wants to be the champions. Nacho Fernandez said that he likes Zinedine Zidane because they are similar in attitude and principles. He is focused on what he has to do.
"I'd have to change 11 players and even that wouldn't work, because I am incapable of playing like that".
"We know about the problems that they have and it's always very satisfying for us to help them out", he said. "He has a good connection with Karim".
It is perhaps a reason why Real are succeeding in La Liga and the Champions League more than their fierce rivals Barcelona, so reliant upon Lionel Messi, Luis Suarez and Neymar for goals and completely lost as those three barely saw the ball at the Parc des Princes against an impressive PSG on Tuesday.
Casemiro's stunning volley crowned a superb display from Real Madrid, who fought back to beat Napoli 3-1 at the Bernabeu in the first leg of their Champions League last 16 tie on Wednesday.
The Neapolitans arrive in the Spanish capital as the top scoring side in Serie A, and 16 of their 57 goals in the Italian top flight have come from Dries Mertens. It has never reached the quarterfinals.
Real Madrid had a minor blip in January, when they lost two games in a row and were knocked out of the Copa Del Rey by Celta Vigo.