Valencia snatched a shock 3-2 win at 10-man Barcelona, dealing a huge title blow to Tata Martino’s side.
Barcelona seemed to be cruising after Alexis Sanchez’s sublime 7th-minute chip, dominating possession until Dani Parejo exploited terrible defending to equalise just before half-time.
Pablo Piatti added a second early in the second half as Valencia again hit Barca on the counter, but the hosts were given a lifeline when Ricardo Costa was incorrectly penalised for handball in the box.
The ball clearly struck the Valencia captain’s shoulder, and with his arm by his side it was a dreadful decision. Lionel Messi equalised from the spot, his first Liga goal since September.
But Valencia would not be denied as Paco Alcacer converted the excellent Sofiane Feghouli’s low cross, with Jordi Alba’s dismissal for a second yellow card forcing Barca to play the final 13 minutes with 10 men.
The result means both Atletico Madrid and Real Madrid can overtake Barcelona atop La Liga on Sunday.
Atletico just need a point at home to Real Sociedad, while Real would go top if they win at Athletic Bilbao and their city rivals fail to beat Sociedad.
It was a strange match played in emotional circumstances following the passing of former Spain boss Luis Aragones, who managed both clubs during his 35-year coaching career.
Several of the Barcelona team played under Aragones, and the team started well, dominating possession and taking the lead when Sanchez clipped an inventive effort over Diego Alves, from a very tight angle.
The hosts continued to pass rings around Valencia, who are stuck in mid-table after a disappointing campaign so far. Sergio Busquets went close from distance, while Messi stung the palms of Alves. Valencia, meanwhile, were limited to occasional counter-attacks, with their best chance a long shot from Feghouli that was well-saved by Victor Valdes.
But Barca paid for their failure to add a second when, not long after Ricardo Costa spurned a free header, two missed tackles from Xavi and Cesc Fabregas allowed Parejo to complete a one-two with Feghouli before finishing past the stranded Valdes just before half-time.
Barca seemed shell-shocked and went behind not long after the restart, as Barca failed to clear a straightforward cross from Antonio Barragan. The subsequent defending was atrocious, as little Piatti was allowed to head past Valdes, who was again stranded.
The officials gave Barca a route back into the match when Costa was adjudged to have handled in the box. It was a woeful call as the defender a. did not handle the ball, b. had his arm down by his side, thus rendering any contact accidental anyway and c. was barely two yards away from the deflection that took it into his midriff.
Messi converted with aplomb, ending a four-month league drought and a four-game dry spell in all competitions.
But Valencia seemed spurred on by the injustice and stepped up a gear. Having been second best, they started to match Barca in possession and deservedly went back ahead when Feghouli raced down the right, picking out Alcacer who finished crisply past Valdes.
There was still half an hour for Barca to come back but they toiled with and without the ball, lacking inspiration as Messi particularly disappointed, while looking very shaky defensively.
Messi did go on one of his trademark mazy dribbles, but he finished wide as Valencia ultimately held on quite comfortably.
It is Barca's second Liga defeat of the season and, with Atletico level on points and Real just one behind, it throws the title race wide open again.