While reigning title holders Madrid were already sure of their first place finish in Group G heading into Wednesday's match at the Santiago Bernabeu, their Russian opponents still had their eye on beating Viktoria Plzen to third place.
Through goals from Fedor Chalov and Georgi Shchennikov, the visitors had a two-goal lead by half-time and Santiago Solari's team had no luck in finding a way back in to the game.
Arnor Sigurdsson had it wrapped up with 15 minutes left, as CSKA became the first team to come away from a trip to Los Blancos with such a scoreline in any continental tournament.
It is the first time Madrid have lost a group stage match at home since October 2009, when AC Milan beat them 3-2 - that was 28 games ago.
0-3 - Real Madrid's defeat against CSKA Moscow tonight is their biggest ever home defeat in European competition. Freezing. pic.twitter.com/KULbCvgJZ1— OptaJose (@OptaJose) December 12, 2018
Although CSKA crashed out of Europe altogether as Viktoria Plzen beat them to the Europa League place with a 2-1 win over Roma, the Russian side can take solace in the fact they are the first team to have beaten Madrid both home and away in the group stages of the competition since Juventus did it in 2008-09.
Madrid will not be too disheartened by their performance, given Solari made big changes to his starting XI for the game. With an average age of 24 years and 100 days, Solari's team was the third youngest Madrid have ever fielded in the Champions League.
Meanwhile, Madrid's highly-rated winger Vinicius Junior made his first Champions League start for the club at just 18 years and 152 days old - Iker Casillas and Raul are the only Madrid players to have started a game in the competition at a younger age.