CSKA Moscow completed a remarkable double over Real Madrid but their 3-0 victory at the Bernabeu proved in vain as they crashed out of Europe.
Goals from Fedor Chalov and Georgi Schennikov had Real two down at half-time in a Champions League home game for the first time since 2000.
Arnor Sigurdsson then confirmed Madrid's heaviest home defeat in Europe with CSKA's third on 73 minutes.
But CSKA's hopes of qualifying for the Europa League were dashed by Viktoria Plzen, who beat Roma 2-1 to finish third behind the Italians and Group G winners Real.
With Madrid already qualified as group winners, Santi Solari picked an inexperienced side as Vinicius Junior, Federico Valverde and Javi Sanchez made their first Champions League starts.
Vinicius Junior was lively in the opening exchanges at the sparsely-populated Bernabeu, while a more familiar name, Marco Asensio, was Real's main threat.
Asensio clipped the top of the bar on 24 minutes and drew Igor Akinfeev into a fingertip save five minutes later as Real applied pressure on the CSKA goal.
Karim Benzema saw a low drive from a corner blocked by Rodrigo Becao on the half hour, but it was not long before Asensio was back in the thick of it as the Spaniard played a one-two with Benzema and fired a shot straight at Akinfeev.
But Real were stunned on 37 minutes when Sigurdsson offloaded the ball to Chalov on the edge of the area, and the striker caressed a sumptuous effort into the far corner past Thibaut Courtois.
It took just five minutes for CSKA to double their lead as Schennikov arrived late on the scene to convert a rebound after Mario Fernandes had drawn Courtois into action.
With Bayern Munich the last side to hold a two-goal advantage at half-time at the Bernabeu 18 years ago, Solari turned to Gareth Bale to salvage the situation.
But with the exception of a chance for Asensio on 55 minutes, which the forward took an age to take before being blocked, Real created very little in front of an increasingly hostile home crowd.
And things took a turn for the worse 17 minutes from time when Sigurdsson slotted a precise shot through bodies into the bottom corner to wrap up a stunning victory for the Russian champions.
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- CSKA Moscow's 3-0 victory over Real Madrid is Los Blancos' heaviest home defeat in any European competition in the club's history.
- CSKA Moscow are the first side since Juventus during the 2008/09 UEFA Champions League campaign to beat Real Madrid both home and away during the group stages of the competition.
- Real Madrid have lost a group stage match at home in the UEFA Champions League for the first time since October 2009, when they lost 2-3 to AC Milan, 28 games ago.
- The average age of Real Madrid's starting XI in tonight's defeat against CSKA Moscow was 24y 100d, their third youngest Champions League starting line-up, and their youngest in the competition since December 2005 v Olympiakos (23d 36d).
- Arnor Sigurdsson is the first player to both score and assist at the Bernabeu against Real Madrid in the UEFA Champions League since Pierre-Emerick Aubemyang did so for Borussia Dortmund back in December 2016.
- Vincius Júnior (18y 152d) is the third youngest player to start a UEFA Champions League match for Real Madrid, with only Iker Casillas (18y 117d) and Raúl González (18y 77d) starting a match in the competition at a younger age than the Brazilian for Los Blancos.
Man of the Match - Fedor Chalov
The centre-forward set CSKA on their way to a famous victory with a well-taken opener and played a key role in their second at the Bernabeu. CSKA didn't get the result they ultimately wanted, but Chalov will be the toast of Moscow.
What's next?
Real Madrid host Rayo Vallecano in La Liga at 5.30pm on Saturday before travelling to the UAE for the FIFA Club World Cup.