Real Sociedad produced a stunning fightback from 2-0 down to beat European champions Real Madrid 4-2. Meanwhile, bitter rivals Barcelona made it two wins in as many games under Luis Enrique with a late winner at Villarreal.
Madrid were without the injured Cristiano Ronaldo and departed Angel di Maria and Xabi Alonso, but still looked on course for a comfortable evening when they flew into a 2-0 lead inside the opening 11 minutes thanks to goals from Sergio Ramos and Gareth Bale.
However, Inigo Martinez and David Zurutuza levelled for the hosts before the break and Zurutuza and Carlos Vela sealed a much-needed win for under-fire Sociedad boss Jagoba Arrasate.
"What happened was very unusual, especially after the first 15 minutes. After that everything was negative, we were horrible in every facet of the game," said Madrid captain Iker Casillas.
Meanwhile, Real boss Carlo Ancelotti placed the blame for the defeat on his players' attitude after going in front.
"It is not easy to evaluate this game because there were two games. In the first half an hour we played with quality, pace and concentration and the other hour we played very badly.Possibly we thought the game was already finished. We conceded fouls, corners, and Sociedad got back into the game. What can I say? We are very sorry because I didn't like that the team played in that way for an hour."
Sociedad had lost their opening game at newly-promoted Eibar and been dumped out of the UEFA Europa League by Russian side FC Krasnodar in midweek and appeared down on their luck after another slow start.
Ramos rose highest to power home Toni Kroos' corner to open the scoring before Bale left Gorka Elustondo trailing with a neat nutmeg and slotted into the bottom corner. But it was the hosts who crucially got the third goal as Martinez slammed home at the far post from Xabi Prieto's flick on. Zurutuza then levelled four minutes before the break as he powered home Alberto de la Bella's pinpoint cross from the left.
Sociedad started the second period the stronger and they got their reward 25 minutes from time when Zuruztuza again timed his run into the box perfectly to connect with Prieto's low cross to the near post. Madrid's humiliation was complete ten minutes later when substitute Carlos Vela appeared to control the ball with his hand before spinning to fire into the top corner.
Barça win late
It was a happier evening for Barça as they were 1-0 victors at Villarreal thanks to 19-year-old Sandro Ramirez's debut goal eight minutes from time.
"It is gratifying to see the young guys score, but the most important thing is the victory," said Enrique. "We kept going until the end. Villarreal defended very well and waited for the counter-attack to cause us problems."
Barça completely dominated possession in the opening 45 minutes, but failed to create clear-cut chances as Sergio Asenjo parried a drive from Pedro before turning a deflected Messi free-kick onto the post. But Villarreal were nearly gifted the lead at the start of the second period as Barça defender Jeremy Mathieu turned Jaume Costa's cross off the outside of his own post.
Barça then upped the pace after Neymar replaced Munir El Haddadi and Asenjo had to be at his best again to turn away a well-struck Messi free-kick. Yet, for all their chances, Barça were inches from being behind moments later when Tomas Pina struck the inside of the post and Javier Espinosa fired the rebound inches wide.
The visitors did finally make the breakthrough eight minutes from time when more fine footwork from Messi provoked another save from Asenjo, but Sandro was on hand to force the ball home from close range. There was still time for a final scare for Barça as Giovanni dos Santos smashed a volley off the post from a narrow angle, but Enrique's men held on to go top of the embryonic La Liga table.
In the day's other matches, Deportivo La Coruna drew 2-2 with Rayo Vallecano, while Elche scored late to draw 1-1 with Granada at home.