Takefusa Kubo scored a stoppage-time winner as Mallorca came from behind to stun Atletico Madrid 2-1 at the Wanda Metropolitano on Saturday.
Matheus Cunha opened the scoring for Atletico in the 68th minute to set Diego Simeone's side on track for three points.
However, Franco Russo levelled in the 80th minute and Real Madrid youngster Kubo silenced the home fans with a 91st-minute goal.
The defeat sees Atletico drop to fourth, with Mallorca climbing to 12th after their fourth win of the LaLiga season.
Atletico's thoughts now turn to Tuesday and a must-win Champions League game against Porto in Portugal.
As well as winning, they also need Milan to fail to beat Liverpool to book their place in the last 16 of the competition.