Tito Vilanova's side are currently eight points clear of Atletico Madrid in second, as they look set to reclaim the La Liga title from Real Madrid.
The defeat for the Catalan club was their first league loss of the season and early in the first half it looked certain that their unbeaten run would continue as they took a 2-0 lead. Sociedad grabbed a goal before the interval before equalising in the second half, setting up an injury-time winner to secure a remarkable comeback.
After the defeat, Barca assistant manager Jordi Roura said he was confident will bounce back.
"I have no doubt that we'll give it our all, but this is football. I'm sure that the team will react well," he said.
Osasuna, third from bottom, welcome new loan signing Francisco Silva as they continue to battle for survival. The Chilean midfielder is on loan for the remainder of the season after joining from Universidad Catolica.
"It's my first experience in European football and I have to adapt as quickly as possible, because time is short and I hope to make the most of it," he told the club's website.
Atletico Madrid travel to Athletic Bilbao as they look to close the gap on the leaders. In the build-up to the game Atletico striker Adrian claimed he was paying little thought to the speculation linking him with a move to Arsenal. A clause in his contract means the 25-year-old is free to leave if a bid is received for 18 million euros (£15.1million).
"I try to isolate myself from the rumours," he said.
"We are used to them and do not take them seriously. I am very happy at Atletico.
"I am happy here and it is my intention to continue here.
"The good thing at the moment is that the team is doing very well. I would like to stay for a while yet."
Bilbao's prized asset Fernando Llorente has agreed a deal to move to Juventus at the end of the season after his contract expires with the Basque club.
Real Madrid's season of struggle continues as goalkeeper Iker Casillas has been ruled out of the game against Getafe. The Madrid captain fractured a bone in his hand during Wednesday's Copa del Rey clash against Valencia and will now have an extended run on the sidelines.
"After carrying out initial x-rays at the La Moraleja Sanitas Hospital it has been confirmed that the footballer Iker Casillas has suffered a fracture at the base of the first metacarpal on his left hand," a statement from the club read.
"It will be assessed again by a specialist later today to decide what treatment will be followed."
There has been no timeline given for the injury, but one of this nature tends to take up to three months to heal.
Sunday's 4pm clash will see Rayo Vallecano and Real Betis battle it out as both teams look to cement claims for a European place come the end of the season, with the home side in sixth four points off their visitors who currently occupy the final Champions League spot.
Relegation-threatened Mallorca will host Malaga, while the Monday night clash will see 16th-placed Granada travel to 12th-placed Sevilla.
Ricardo Costa's stoppage-time header decided a topsy-turvy encounter in Valencia's favour as Deportivo La Coruna lost 3-2 and finished with nine men.
The match was all-action from the outset, Jonas' looping header after just 31 seconds putting Los Che ahead before Riki's brace gave Deportivo a half-time advantage.
Silvio's needless dismissal seven minutes after the restart changed the course of the game, though, as Nelson Valdez equalised and then Costa bagged a dramatic late winner - to lift Valencia to fifth - before Paulo Assuncao's red card rubbed further salt in the hosts' wounds.
There was also late drama at the Ciutat de Valencia, where Antonio Rukavina's stoppage-time own goal handed Levante a come-from-behind 2-1 triumph over Real Valladolid.
Javier Baraja had given the visitors an early lead with a sweetly struck volley but Levante equalised two minutes before half-time through Jose Barkero's fine curling free-kick.
Then, in added time, Valdo miscontrolled Obafemi Martins' pass but the loose ball struck Rukavina and deflected past the helpless Dani Hernandez and into the net.
Elsewhere in La Liga on Saturday, Real Sociedad stretched their impressive run to just one defeat in 11 league games but were unable to make their numerical advantage count as 10-man Celta Vigo held on for a 1-1 draw at Balaidos.
Michael Krohn-Dehli had given the hosts the lead with a wonderfully worked goal on 32 minutes but Celta were forced onto the back foot just after the break when Augusto Fernandez received a second yellow card for a handball.
Gorka Elustondo then brought Sociedad level with a powerful header from Gonzalo Castro's corner just before the hour mark, but the visitors failed to create many more clear-cut chances in the final half-hour and remained five points off the top four.
Finally, Espanyol continued their impressive revival under coach Javier Aguirre with a goalless draw at Real Zaragoza in a match of few clear-cut opportunities.
Both teams finished the match with 10 men as Espanyol's Javi Lopez and Cristian Sapunaru of Zaragoza were sent off in the closing stages.
Saturday's La Liga Results
Sunday's La Liga Fixtures
Monday's La Liga Fixture
Sevilla vs Granada