In a weekend of surprise results in La Liga Barcelona were the latest victims as they missed the opportunity to go top of the league by losing to David Moyes' Real Sociedad side.
Barcelona coach, Luis Enrique announced a shock lineup when he decided to leave both Lionel Messi and Neymar on the bench for the trip to the Anoeta.
Sociedad got off to a perfect start when after just two minutes when Sergio Canales received a short corner on the right and crossed to the near post where Jordi Alba headed into his own goal to give the home side the lead.
Barca responded by taking the game to the hosts but without Messi and Neymar they were struggling to break down a well organised defence.
On twenty minutes, Martin Montoya was taken down by Gonzalo Castro on the edge of the box but Xavi shot over the bar when the costless kick might have been better for a left footer.
Five minutes later Luis Suarez broke away and was able to release Pedro in the left side of the box but he blasted his shot high over Geronimo Rulli's crossbar.
On twenty-seven minutes Xavi released Montoya down the right but his cross was inches away from Munir at the near post.
Barcelona were unlucky not to be given a penalty just after the half hour mark when an Alba cross was deflected off Ion Ansotegi and onto the arm of Inigo Martinez. It looked a sure penalty but the referee wasn't interested.
Sociedad were struggling to get out of their half but on a rare foray into the Barca half they almost doubled their lead. Alberto De La Bella got behind the Barca defence and drilled a low cross in which Xabi Prieto was inches from converting.
Sociedad were starting to get confident and missed another chance when Canales turned Montoya with a superb drop of the shoulder before blasting his shot at Claudio Bravo.
Just before half time Xavi took a short costless kick to Pedro whose shot from all of thirty yards was straight at the goalkeeper but Rulli looked far from comfortable and ended up stopping it with his legs to ensure Real Sociedad were 1-0 up at half-time.
Unsurprisingly, Messi came on at half time for Munir. The young man had never really got going in the first half as Barca struggled against a solid home defence.
Barcelona were lucky on fifty minutes when Jeremy Mathieu came through the back of Castro but the referee didn't believe it was worthy of a second yellow card much to the dismay of the home crowd.
Once again Barcelona were pushing forward in numbers but they were struggling to open the Basque side and Andres Iniesta was reduced to a speculative effort from outside the box on the hour which rose high over the bar.
Seconds later Sociedad should have gone two up when De La Bella crossed and Bravo completely missed it but Xabi Prieto was only able to put his header high and wide with the goal at his mercy.
On sixty-four minutes Barcelona were given another opportunity to score from a set piece when Neymar who had come on for Pedro was brought down by Markel Bergera. Messi took this one but it had the same result as Xavi's effort in the first half, sailing over Rulli's bar.
Minutes later Barcelona had a good opportunity when Iniesta played the ball to Alba on the left who found Xavi running into the penalty area but his weak shot was straight at Rulli.
On seventy-one minutes an Alba pass was met by Suarez who flicked the ball to Messi but his volley went well over the bar as Barcelona continued to struggle to break down the Sociedad back line.
Barcelona were really pressing forward by this stage but Rulli still wasn't being challenged in the Sociedad goal as the defence stood firm.
Barca finally broke the Sociedad backline on eighty-six minutes when Messi played Suarez in. The Uruguayan tried to round the keeper but Rulli got a hand on it to knock it away and deny Barca the equaliser.
Barca continued to push for the equaliser but Sociedad were resolute in defence and managed to hang on to win courtesy of Jordi Alba's own goal.
Sociedad were well worth their win and it is clear to see that David Moyes has made an impact by adding organisation and toughness to their defence.
Barcelona must now look at themselves and try to work out what is going wrong as they failed to take advantage of Real Madrid's defeat earlier on Sunday. Luis Enrique doesn't have much time to find those answers though as they host Atletico Madrid next week in what now looks like a must win game for the Catalans.