Beating the Spanish giants on their own soil sent a message to the rest of Europe that City were now a force to be reckoned with.
And it was all the more impressive because Pep Guardiola's men initially fell behind at the Bernabeu.
Isco put Los Blancos ahead on the hour, but Gabriel Jesus bravely levelled on 78 minutes.
Kevin De Bruyne then made it 2-1 from the spot five minutes later and had Sergio Ramos not pulled Jesus down when through on goal, it could have been even better.
Ramos was dismissed as a result - but few realised that as the pandemic started to grip the world, the second leg wouldn't be played for some six months!
The entire 90-minutes from that famous night is available to watch on CITY+ and you can watch the best of the action for free in the video above.