Ronaldo didn't practice early this week because of a minor ailment, but he returned to action on Tuesday and was ready to face Napoli in the first leg at the Santiago Bernabeu Stadium on Wednesday.
Two more chances fell Madrid's way before the final whistle.
The 30-year-old acknowledged that he is grateful for reaching 500 matches with the record European football champions Real Madrid.
With Gareth Bale not fully fit and Karim Benzema still struggling, it will be Cristiano Ronaldo again carrying the load for Real Madrid in the Champions League.
"Napoli are a good attacking side and they play with a lot of intensity and speed".
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Real Madrid look comfortable at the top of the table and with a couple of games in hand they'll be confident of securing the La Liga title.
Madrid had won 23 of their previous 32 home matches against Italian opposition, yet their only two-legged victory over a team from the peninsula came last season against Roma, also in the round of 16.
"We must go step by step, game by game".
The frantic pace of the match had evaporated in the closing 10 minutes, with both teams suffering with fatigue and mental tiredness. Madrid recognized that Napoli were having issues with wide attackers cutting in, and Cristiano Ronaldo used that to his advantage, taking the previously-impressive Kalidou Koulibaly to the touchline and turning him inside-out before slipping a flawless assist in to Toni Kroos. There is a high level of pressure on every player, but it will help them stay 100 percent concentrated in every game. But in order for the Partenopei to progress past this round for the first time, they must try and stop Los Merengues from scoring for the first time in 34 Champions League home games.
It was a lovely response for Napoli and one that will be treasured for a long time.