Barcelona's hopes of retaining their La Liga crown suffered a further blow with a 3-2 loss away to Osasuna.
The hosts got off to an ideal start at Estadio Reyna de Navarra.
In the fourth minute, Raul Garcia received the ball on the edge of the 18-yard box and flicked it on to a sprinting Dejan Lekic, who buried his strike past Victor Valdes to open scoring.
Pep Guardiola's men attempted to fight back but struggled to establish their quick, one-touch passing game on the frozen pitch.
The hosts declined to sit back and defend their lead, soon finding themselves 2-0 ahead.
After being picked out by Garcia on the right flank, Alvaro Cejudo looped in a cross which found the surging Lekic, and the Serbian tapped past Valdes for his second of the match.
The first half ended with Barca beginning to dominate possession, but they proved incapable of forcing a meaningful attempt on goal.
Barcelona did pull one back five minutes into the second half, with Isaac Cuenca responsible.
The half-time substitute centred a cross from the right and found Alexis Sanchez unmarked, with the Chile international sliding the ball past Osasuna goalkeeper Andres Fernandez.
But the home side soon had a third goal when Garcia netted to give Osasuna a decisive advantage.
The reigning champions refused to give up without a fight, as another substitute, Christian Tello, made it 3-2 with 18 minutes remaining.
After being picked out on the right, Tello beat his marker before blasting past Fernandez from close range.
Barca looked to have equalised when Alexis found the back of the net after Lionel Messi's cross, only for the goal to be ruled out for offside.
The heavyweight visitors continued to press their opponents right up until to the final whistle, but they could not find an equaliser and stumble to their second defeat of the league season.
Following the loss, Barca could find themselves 10 points adrift of top spot if Real Madrid beat Levante at home on Sunday.
In other matches, Nelson's 91st-minute strike saw Real Betis snatch a 2-1 win at home to 10-man Athletic Bilbao.
Ruben Castro opened the scoring for hosts Betis 10 minutes into the match Estadio Benito Villamarin, with Javi Martinez pulling one back for Athletic.
Athletic were reduced to 10 men when goal-scorer Martinez committed a second bookable offence in the 64th minute.
Finally, Racing Santander played out a 0-0 draw in their match at home to Atletico Madrid.