A disappointing afternoon for Barcelona was compounded by potentially serious injury to Gerard Pique, who was forced off following a freak collision with Atletico Madrid star Angel Correa.
Needing a positive result at the Wanda Metropolitano to kick-start their spluttering Liga campaign in 2020-21, Barca instead fell behind just before half-time due to a horrendous mistake from Marc Andres ter Stegen.
The Germany goalkeeper was caught far from his net and rounded by Yannick Carrasco, who was left with an easy finish into the open net to put Atleti in the ascendance.