The decision to have an away section above the home fans was shown up in dramatic fashion as bottles and objects rained down on Real Madrid's celebrating players.
Los Blancos had just overcome their city rivals yet again in the Champions League when things got nasty post-match.
A lifeless performance from the visitors ended in a penalty shoot-out win, but running to their supporters post-match, it was clear the drama wasn't over.
As those in white began jumping around in celebration, the fans in red and white started aiming objects, with one bottle heading towards Jude Bellingham.
Registering the projectile early, the England megastar hilariously jumped up and headed it away, making the fuming home fans even more upset.
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That wasn't the only heated moment from the celebrations, though, with Antonio Rudiger potentially landing himself in hot water.
The former Chelsea man, who scored the winning goal in the shoot-out, appeared to make a cut-throat gesture towards the Atleti fans, an act AS called 'deplorable'.
Meanwhile, Vinicius Jr, who was surprisingly substituted off just before the shoot-out, also wound up supporters by pointing at the 15 Champions League wins patch on his shirt.
The incidents occurred moments after record winners Real booked a quarter-final spot against Arsenal.
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The hate between themselves and Atleti is clear for all to see, and it's not the only flashpoint this season, with a LaLiga derby at the same ground suspended for ten minutes in September when objects were thrown at Real's Thibaut Courtois.
The Belgian, formerly of Atleti, had goaded the home fans after Eder Militao's opener, but Atleti eventually secured an equaliser and still remain in the title fight.
Atleti manager Diego Simeone received criticism post-match for saying Courtois played his part in the stoppage, calling him a 'provocateur' while they also clashed on pitch.
Exchanges between himself and Real players are nothing new, though, and there was another one after the most recent defeat.
The shoot-out saw former Manchester City striker Julian Alvarez denied his goal through a slip and double touch of the ball from the spot.
Responding to the incident post-match, Simeone said: "When Julian plants his foot and kicks, the ball doesn't move even a little bit.
"But if VAR called it, I've never seen a penalty called by VAR, but it's still valid, and they'll have seen that he touched it. I want to believe they'll have seen that he touched it."
Simeone went on to ask the room to raise their hands if they saw the double touch.
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Currently injured Real midfielder Dani Ceballos spotted that someone had posted the clip with the caption 'cinema' and re-posted it himself with a raised hand emoji.
The two already clashed this campaign after refereeing controversy in Real's 5-2 Copa del Rey win over Celta Vigo, when Simeone said: "It's happened for the past 100 years, I don't know why anyone's surprised."
Ceballos responded: "He hasn't got over the two [Champions League] finals he lost against Madrid," but then Simone left the midfielder red-faced.
The Argentine commented that Ceballos felt the same when he wasn't a Madrid player, and then some awkward quotes were brought up from his time at Real Betis where he said referees, 'Always make mistakes for the same side'.