European champions Real Madrid surrendered a two-goal lead established after just 11 minutes as they crashed to a shock 4-2 defeat at struggling Real Sociedad.
Madrid had looked set to sweep Sociedad aside as they struck twice early on through Sergio Ramos and Gareth Bale and also hit the woodwork.
The visitors had a number of other chances to increase their lead before Sociedad staged a stunning comeback that saw them to victory thanks to Inigo Martinez (36), David Zurutuza (41 and 65) and Carlos Vela (76).
That earned Sociedad their first points of the season and came at the end of a week that had seen them beaten by newcomers Eibar last weekend and knocked out of the Europa League by Krasnodar on Thursday.
Those results increased the pressure on coach Jagoba Arrasate, who then saw Madrid made a blistering start to Sunday's clash at the Anoeta.
Carlo Ancelotti's men, who were far from impressive in beating minnows Cordoba at home last week, were without the injured Cristiano Ronaldo and saw Angel di Maria and Xabi Alonso sold this week -- but they could hardly have been more impressive in the opening stages.
There were just five minutes on the clock when Ramos got on the end of Toni Kroos' inswinging corner to send a glancing header in off the far post, and he came within inches of making it 2-0 four minutes later with a brilliant free-kick that came back off the bar.
Madrid need not have worried, though, as moments later Bale doubled their lead, the world's most expensive player picking up a pass from Luka Modric before nutmegging Gorka Elustondo and drilling a low shot inside the near post.
Rampant Madrid had further opportunities to increase their lead, with Ramos heading over and Marcelo and Kroos denied by brilliant saves from home keeper Enaut Zubikarai.
At the other end, Sociedad had produced little to worry Madrid in the opening half-hour apart from a thunderous shot from Esteban Granero that was superbly blocked by Ramos.
However, the hosts got a foothold in the match when Martinez escaped Ramos at the far post to slot home from a corner -- and five minutes later the Basque side were back on terms when Zurutuza thundered home a header from near the penalty spot.
Madrid were shellshocked but almost re-took the lead before the break as Ramos beat two defenders and the goalkeeper to a James Rodriguez free-kick, only to see his header go inches wide.
The second half proved one to forget for Ancelotti's all-stars as Sociedad scored twice in the space of 11 minutes to take the win.
Good work between Xabi Prieto and Sergio Canales saw Madrid opened up down the right, and the former's low cross was fired into the roof of the net by the sliding Zurutuza.
Madrid barely had a chance to draw level before they found themselves 4-2 down in controversial fashion, the visitors claiming Vela had brought the ball down with his arm before lashing a left-footed shot past Casillas.
Madrid had opportunities to set up a frantic finale but Sami Khedia headed over, Zubikarai denied Rodriguez and Karim Benzema hit the outside of the post as they left San Sebastian empty-handed.