Los Blancos created chances throughout the contest, however second-half goals from Luis Suarez, Lionel Messi and Aleix Vidal gave the visitors all three points.
Not only does the result leave Real fourth in La Liga, behind Barca, Atletico Madrid and Valencia, but it's also ramped up the pressure on Zinedine Zidane's future at the club.
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The reigning Spanish, European and world champions desperately need to rediscover their best form in 2018, in which we'll see them battle Paris Saint-Germain in a mouth-watering tie.
If Real fans weren't feeling bad enough already, what ex-player and current PSG star Angel di Maria did on social media following the match is sure to make matters worse.
Di Maria at Real Madrid
Di Maria spent four years at the Bernabeu between 2010 and 2014, scoring 36 goals in 190 appearances and developing into a world-class attacking midfielder.
After a failed season at Manchester United, the 29-year-old joined PSG, and whilst he key to Real's 2013-14 Champions League triumph, he has now well and truly angered their fans.
Di Maria's Instagram activity
The Argentinian caused a big stir on Sunday after 'liking' a number of photos on Instagram related to Barca players celebrating their victory over his former club.
As you can see in the image below, the eight pictures that Di Maria 'liked' included Leo Messi's goal celebrations as well as Barcelona's dressing room team photo after the game.
Madrid fans react on Twitter
Given that Sergio Aguero also featured in Di Maria's 'likes', it's a possibility that he was simply trying to send out congratulations to his international teammate Messi.
However, he should've known better than to 'like' Barca-related content in such public fashion, and it's safe to say his former Madrid supporting fanbase are fuming with him.
Check out some of the reaction from Real fans below:
So, Real Madrid fans aren't happy, and neither is Di Maria, given that world-record signing Neymar has seriously limited his playing time this season.
Ahead of next summer's World Cup, there are rumours that he could leave Paris in January, with none other than Barcelona reportedly interested in the winger.
What do YOU make of Di Maria's Instagram activity after Real's El Clasico loss? Leave YOUR opinion in the comments box below!