Barcelona slipped to a second consecutive defeat for the first time since April 2012 as they lost for the first time in the league this season 1-0 away to Athletic Bilbao on Sunday.
Barcelona had suffered their first defeat under coach Gerardo Martino against Ajax in midweek and Athletic appeared to learn from the Dutch champions' approach as, without the injured Lionel Messi, Barca struggled to impose themselves on the game.
Iker Muniain slotted home the only goal of the game from Markel Susaeta's cross 20 minutes from time as a third straight win moved the Basques into fourth.
The Catalans remain top of La Liga on goal difference only from Atletico Madrid with Real Madrid now just three points behind the leaders.
Neymar had Barcelona's best effort of the first-half with a curling effort that was brilliantly tipped over the bar by Gorka Iraizoz.
However, it was the hosts that had the better of the chances before the break as Muniain fluffed his lines after Andoni Iraola's cross was deflected perfectly into his path before Gorka Toquero headed wide when unmarked from Muniain's cross.
Martino's men improved after the break as Athletic's pressing wavered slightly and Neymar should have given them the lead when he raced onto Cesc Fabregas' fine through ball but slipped as he shot and the ball sailed well over.
Barca were then left infuriated at referee Juan Martinez Manuera only showed Ander Iturraspe a yellow card when he pulled back Neymar as the Brazilian bore down on goal.
Neymar pulled himself up to take the resulting the free-kick which curled inches wide of Iraizoz's right-hand post.
However, it was Athletic who finally made the breakthrough when Ander Herrera robbed the ball deep inside Barca territory and fed Susaeta whose cross from the right was turned home by Muniain for his third goal of the season.
Toquero then passed up a great chance to make it 2-0 as he headed straight at Jose Manuel Pinto from Munain's inch-perfect cross.
Martino surprisingly withdrew Xavi and Andres Iniesta for Sergi Roberto and Pedro Rodriguez respectively in his search for an equaliser.
But Athletic saw the game out comfortably to register their first win over Barcelona since 2006.