Barcelona suffered their second straight Primera Division defeat after losing 1-0 at Real Sociedad.
Mikel Oyarzabal's header in the fifth minute separated the two sides, meaning Barca have not won at Anoeta since 2007.
The surprise defeat means Luis Enrique's side have now gone three league games without a win as the title race was blown wide open.
Barca rested most of their senior players as they look to seal a Champions League semi-final place when they face Atletico Madrid in midweek before hosting Valencia on Sunday.
The win sees Eusebio Sacristan's side climb one place up to ninth.
Atletico rallied from a goal down to beat Espanyol 3-1 and keep their title chances alive as they cut the gap on Barca to three points.
Pape Diop's headed goal from a corner had put the Catalans ahead after 28 minutes but Fernando Torres grabbed a third goal in as many games to level before the break.
Antoine Griezmann's arrowed finish early in the second half completed the comeback with the Frenchman becoming the first player since Diego Forlan in 2009 to score in seven successive La Liga matches.
Koke added a third late on as Diego Simeone's men gained confidence ahead their Champions League second-leg against Barcelona on Wednesday.
Real Madrid produced a dominant performance to respond to their shock defeat at Wolfsburg as Cristiano Ronaldo scored and provided two assists in a resounding 4-0 win over Eibar.
James Rodriguez opened the scoring from a free-kick after just four minutes. Lucas Vazquez and Jese added to the scoring with the help of passes from Ronaldo, who grabbed Madrid's third of the afternoon to move on to 30 Primera Division goals for the season.
The win kept the pressure on title rivals Atletico and Barcelona, with Zinedine Zidane's side trailing the latter by four points thanks to a sixth consecutive league victory, while Eibar stretched their winless run to eight games, although the Basques remain in mid-table.
Despite the manner of their win, the home fans, still frustrated from their Champions League defeat, vented their anger at Danilo when he was brought on in the second half, greeting the Brazilian right-back with a cacophony of boos following his much-criticised performance against Wolfsburg.