Real Madrid suffered a 4-2 defeat at the home of their local rivals after extra-time with Antoine Griezmann and Rodrigo Riquelme getting the decisive goals.
It was an uncharacteristically bad night for Carlo Ancelotti's side, who suffered the setback four days after achieving Spanish Super Cup glory.
Clumsy defending for Griezmann's goal and the strikes in normal time by Samuel Lino and Alvaro Morata cost the Spanish giants in a miserable night at the Wanda Metropolitano.
But Bellingham, who's made an electric start to life in the Spanish capital, impressed once again despite failing to add to his tally of 17 goals for the club.
He supplied the assist for Joselu's 82nd-minute equaliser after combining well with Vinicius Jr, a goal which took the game to extra time.
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There were a number of impressive runs from Bellingham, including early on in the contest when he beat two Atleti players, getting past one with a clever nutmeg before his shot was deflected onto the crossbar.
And these fans are in no doubt the Real Madrid no.5 was the game's standout player despite being on the losing side.
One fan said: "Best player on the pitch, he was let down."
Another said: "Jude Bellingham gave absolutely everything, he never stopped trying. He was genuinely let down tonight."
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This fan added: "Jude Bellingham gave everything on the pitch tonight. Thank you."
While this one claimed: "Bellingham was let down today. He was the best player on the pitch."
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