Osasuna dealt a further blow to Barcelona's title hopes by inflicting a 3-2 defeat at Estadio Reyno de Navarra on Saturday night.
Two goals from Dejan Lekic had the home side in control at half-time - but Alexis Sanchez pulled a goal back six minutes into the second half.
Raul Garcia made it 3-1 to the home side five minutes later before substitute Cristian Tello netted a second for Barcelona 17 minutes from the end.
There were several clear chances at both ends and a disallowed goal for the visitors - but Osasuna held on for victory to leave Barcelona still seven points adrift of leaders Real Madrid, who play Levante at home on Sunday.
It means Pep Guardiola's men have now dropped 16 points on their travels in the Primera Division this season.
Atletico Madrid passed up a host of good opportunities as Racing Santander clung on to claim a point from a goalless encounter at El Sardinero.
The visitors had the best of a largely uneventful first half but Adrian Lopez passed up their best opportunity as he fired straight at Tono Ramirez.
The Racing keeper was busier after the break as he repelled efforts from Felipe Luis and Diego, whilst the latter and Radamel Falcao also struck the post.
Atleti have now gone six games under Diego Simeone without conceding but they will be disappointed with a second consecutive 0-0 draw from a game in which they were rarely troubled.
Right-back Nelson hammered an injury-time winner to give Real Betis a 2-1 victory over 10-man Athletic Bilbao.
Nelson, playing his first Primera Division match of the season and recently back from compassionate leave after his father died, drove the ball home from the edge of the box to seal the points for Betis, who moved up to 12th.
Ruben Castro had put Betis ahead in the 10th minute before Athletic levelled 13 minutes later through Javi Martinez, who was then harshly sent off in the 64th minute.
If the sending-off was tough on the Copa del Rey finalists, who would have moved into the Champions League places with a win, the scoreline was not as Betis were the better side throughout.