Promoted Alaves dealt champions Barcelona a shock 2-1 defeat at the Nou Camp on Saturday while Cristiano Ronaldo returned from injury to help Real Madrid thrash Osasuna 5-2 and go two points clear at the top of La Liga.
With Lionel Messi, Luis Suarez and Andres Iniesta on the bench, Barcelona went behind to the visitors in the 39th minute before Frenchman Jeremy Mathieu equalised in the 46th. Ibai Gomez then scored the winner in the 64th.
Ronaldo, who had been out for two months with a knee injury, scored six minutes into his return as Zinedine Zidane's Real equalled the club's 1960-61 record of 15 successive league victories.
The result left Real Madrid with nine points from three games, while Barcelona are fourth on six. Sevilla went second on seven points after beating third-placed Las Palmas 2-1.
Atletico Madrid are fifth on five points after beating Celta Vigo 4-0 to earn their first win of the season.
Having seen their two main title rivals win, the pressure was on Barcelona to see off opponents who drew with Atletico at the Vicente Calderon on the season’s opening day.
But with their top players rested by coach Luis Enrique after returning from international duty, long-haul flights and injury, Barcelona struggled to get going.
New signing Paco Alcacer barely touched the ball in the first half and fired his only chance wide of the far post early in the second, while Ivan Rakitic spurned two good chances.
Neymar was the only one of the MSN (Messi-Suarez-Neymar) trio to start, although he ended the game with the others by his side, but Barcelona still failed to create any more clear opportunities.
"I’m the most responsible for what happens," Luis Enrique told reporters after the game. "It’s easy to judge what happens with the benefit of hindsight.
"From this clash we will take good things forward. We did not generate our usual chances and (Alaves) were very accurate. It’s an ugly result for us but you have to congratulate the opposition."
Real Madrid had plenty of chances and were 5-0 up before Osasuna replied in the second half.
Ronaldo, who reiterated afterwards that he wants to see out his career at Real, started the rout by knocking home an inviting cut-back from Gareth Bale.
Goals from Danilo and Sergio Ramos then sent Madrid 3-0 up before the break.
Pepe and Luka Modric were also on target in the second half before headers from Oriol Riera and David Garcia provided some consolation for the visitors, who saw Roberto Torres miss a 73rd minute penalty and Cayetano Bonnin sent off in the 80th.
Zidane took the Portuguese forward off in the 66th minute to protect him as Ronaldo continues his comeback from the knee injury sustained in the Euro 2016 final.
"Like everyone I enjoy seeing [Ronaldo] on the pitch, I always want him with me," said the Frenchman.
"He played for an hour today, we will see what happens on Wednesday (against Sporting in the Champions League]. I have not negotiated anything with him about his playing time.
"It has been 60 days without competition and now we have seven games in three weeks. So we must be aware of that."
One more La Liga win would equal Barcelona's 2010-11 record of 16 in a row.
In the day’s other game Villarreal won 2-0 away at Malaga with goals from Jaume Costa and Nicola Sansone.
