Atletico Madrid's unbeaten start to their LaLiga title defence came to an end as Victor Laguardia's early goal proved decisive in a 1-0 win for struggling Deportivo Alaves.
Alaves headed into Saturday's early game having lost all five LaLiga matches in 2021-22, yet they overcame the champions to claim a first top-flight win over Atleti since 2003.
Laguardia was the crucial figure. His fourth-minute header gave Alaves the lead, and the 31-year-old also made a vital clearance off the line in the second half.
Mamadou Loum and Tomas Pina squandered golden chances to make sure of the points for Alaves, but Diego Simeone's team could not make their fortune count as they tasted defeat in LaLiga for the first time since April.
Javier Calleja made five changes from the side that lost to Espanyol in midweek, but it was the ever-reliable Laguardia who headed Alaves in front when he escaped Stefan Savic to meet Ruben Duarte's corner.
Laguardia almost cost Alaves with a poor clearance before the half-hour mark, though Marcos Llorente was unable to direct his effort on target in Atleti's only first-half sighting of goal.
Rodrigo de Paul and Llorente tried their luck from range to no avail, before Laguardia came to Alaves' rescue with an exceptional piece of defending.
Alaves' goalscorer judged that De Paul's free-kick was curling in, and just got back in time to head the ball off the line.
Sloppy defending from Felipe allowed Loum in at the other end, only for the Alaves midfielder to blaze over from close range.
Simeone turned to Angel Correa to offer some inspiration, and the forward soon wriggled free in the area to get a shot off, but Fernando Pacheco made an excellent stop.
After Pina missed a glaring chance, there was drama at the last, with Atleti wanting a penalty for handball.
Referee Antonio Miguel Mateu Lahoz initially appeared to point to the spot, but instead it was the final whistle that went, and Alaves held on for a deserved win.