Barcelona suffered a shock loss to lowly Almeria as the leaders' 13-game unbeaten run in LaLiga came to a grinding halt in a 1-0 reverse.
El Bilal Toure's first-half strike proved the difference as the Mali international latched onto a Luis Suarez ball looped into his path and cannoned a finish in off the crossbar at Power Horse Stadium on Sunday.
On the back of their Europa League exit to Manchester United on Thursday, Xavi's side suffered a second successive defeat for the first time this season, missing the chance to go 10 points clear at the summit.
But opposite number Rubi will cherish a famous win for his side, as their upset helped to hoist them out of the relegation zone at the other end of the table.
Determined to ensure there would be no hangover from their midweek European loss, Barca looked to dominate possession from the first kick of the ball.
Yet they could not make their early chances stick and paid the price when Suarez brought down a long ball on the right flank, before lobbing a cross inside for Toure to finish via the woodwork in the 24th minute.
The visitors laboured in pursuit of an equaliser for the rest of the half, and headed into the interval looking no closer to finding the answers.
With the need to muster a response pressing, Barca again sought to pile on the pressure after the break, restricting their hosts to defensive duties and a meagre share of the ball.
But, with Robert Lewandowski placing two headers off target in the final 15 minutes, they could not summon the magic moment to save them from a stunning defeat.