One of the only downsides to emerge from their triumph in Bavaria was Gareth Bale being withdrawn in the second half after complaining of a niggle. "The belief is still strong, or we wouldn't be FC Bayern Munich", he said.
Ronaldo struck twice in the second half to secure the valuable victory after Bayern had led through Arturo Vidal, who also missed a penalty at the end of the first period. "We've won the first match, the second is still to come", he added.
"A tie is never decided in the first leg, but we played a good match".
Zidane's men are away to Sporting on Saturday, a match which will be followed by two crucial games in the space of a week.
He had to wait a little while before reaching a century however - Ron's first goal of the night ended a seven-month CL goal drought, having last scored against Borussia Dortmund in September 2016.
They've failed to score in three of their four trips to top-five ranked sides since 2013/14, with two of these seeing fewer than two goals and since Real don't need to win, this could prove a low-scoring encounter.
Real Madrid has heavily dominated the 10-men Bayern Munich but the Manuel Neuer denied any casualty after the second goal.
"For that reason we are very happy when these games come at the end of the season".
Ancelotti hopes to have striker Robert Lewandowski, who missed the first leg with a bruised shoulder, and defender Mats Hummels both back for the return in Madrid. Zidane said he wasn't sure if Bale would be ready next week to play Bayern in the return leg of the quarterfinal.
Ronaldo has scored 28 goals in 37 appearances for his club this season.
Yet Real remain at La Liga's summit and with the upper hand in their Champions League quarter-final, proving that even a Ronaldo performing below his best may be enough to win some of the biggest accolades in European football. The second half is hard to judge.
It was Madrid's Taliman Cristiano Ronaldo again to the rescue. "We had the game under control in the first-half, but we lost our efficiency after the break".
Madrid responded soon after the interval and a red card to Javi Martinez made life easier for Zinedine Zidane's side before Ronaldo scored his second 13 minutes from time.