The Catalan giants failed to sustain their hugely impressive start to the match, after two second-half goals from the Basque club consign them to a disappointing drawBarcelona surprisingly blew a two-goal lead at the Anoeta to draw 2-2 with Real Sociedad on Saturday.
Despite starting goals from Xavi and Cesc Fabregas gave the visitors a commanding early lead, the hosts came back against the odds thanks to an Imanol Agirretxe header and an Antonie Griezmann strike.
The champions came into the fixture in San Sebastian on the back of a five-goal rout against Villarreal a fortnight ago, and despite an international break being sandwiched in the way, they began to dazzle their opponents with their award-winning brand of visionary, cutting-edge football.
It took just 10 minutes for the Catalans to register the opening goal, thanks to Xavi, after Fabregas' delightfully scooped pass over the hosts' defence found Alexis Sanchez in the box, who squared the ball into the path of the playmaker, who tapped in from close range.
Barcelona's lead was doubled moments later, as a near repeat of the move for the first goal was executed once again, with Xavi's lobbed through ball dropping in front of Fabregas, who ensured their efforts counted by sliding a rebound into the back of the net, after Sanchez originally failed to beat Claudio Bravo one-on-one from the ex-Arsenal man's cut-back.
The 'tiqui-taca' style football ensued for the remainder of the first half, and it seemed that Pep Guardiola's men would proceed to see the game out with little trouble. However, the second 45 saw a much-improved performance from Real, as they started to step up their search for a route back into the match, and they were soon aptly rewarded.
Agirretxe was the man who gave the Basque outfit a fighting chance for a reprieve on 59 minutes, after Xabi Prieto's corner met the hitman, who turned away from his marker to nod a powerful header past Victor Valdes.
Incredibly, the equaliser was found just two minutes later, albeit in rather acromonious circumstances, as David Villa's bizarre pass-back from an advanced position on the right horribly landed in the path of Agirretxe, who went on to shift past an on-rushing Valdes and chip the ball at goal.
Sergio Busquets parried the effort onto the crossbar on the line, but the promising French flanker Griezmann managed to net the rebound, as they successfully saw out the course of the encounter to give Real Madrid the initiative, as they face Getafe later on Saturday.