Real Madrid sank to a shock 1-0 defeat by Alaves on Saturday after a 95th-minute winner from Manu Garcia consigned the European champions to a fourth game without victory.
It is four games without a goal too for Julen Lopetegui's side, their longest scoring drought since 1985, as Garcia headed home to send the Mendizorrotza Stadium wild.
Alaves fans ran onto the pitch to celebrate their famous win and the chants continued long after the final whistle blew.
For Madrid this was another body blow and to make matters worse, Gareth Bale, their chief forward threat, had hobbled off injured late on. He missed the Champions League loss to CSKA Moscow on Tuesday with a groin strain.
Karim Benzema, out of form and bereft of confidence, was off too after being substituted at half-time but it was Thibaut Courtois at fault for the goal. He came for the cross but failed to claim.
Alaves' excellent start to the season saw them move up to third, level on points with Real.
Bale had been passed fit to start while Luka Modric and Sergio Ramos returned after being rested against CSKA. Courtois took over from Keylor Navas in goal.
The first half was a fight, full of heavy touches, tussles and collisions but largely vacant of clear-cut chances.
Ramos was at the heart of the battle as he clattered Jonathan Calleri and then elbowed the Alaves striker in the face. The referee deemed it accidental but Calleri clearly did not and responded soon after with a late clip on the defender's leg.
Bale span in behind, backheeled to Benzema who teed up Dani Ceballos to shoot, before Benzema had a header volleyed off the line by Victor Laguardia.
But Alaves grew into the half and it took Raphael Varane's diving header to prevent Ibai Gomez from tapping in at the back post.
Benzema was hauled off at half-time and Mariano Diaz instantly looked more dangerous. Only a dangling Laguardia leg ended his weaving run in the penalty area while Real right-back Alvaro Odriozola was slipped in behind but failed to find a team-mate with the pull-back. Lopetegui threw his arms up in frustration.
The rain came down, the whistles grew louder as Madrid dominated possession but Alaves could have won it sooner when Jony sprinted clear, only to drag his finish wide.
Bale went off and another Alaves chance came in injury time. Courtois came for a cross but failed to gather, allowing Garcia to head in a dramatic winner.