Philippe Montanier's side had earlier been replaced in the final Champions League spot by Valencia, who were 1-0 winners over Getafe courtesy of Jeremy Mathieu's goal just before half-time.
But Sociedad responded by coming from a goal down to beat Sevilla. Ivan Rakitic gave the hosts an 11th-minute lead but put through his own net six minutes later to level the scores again.
Sociedad then got their noses in front with Imanol Agirretxe's 26th-minute strike and they stayed there, to return above Valencia in the standings with two matches remaining.
Granada, meanwhile, took a huge step towards securing their La Liga status with a 3-0 victory over fellow strugglers Osasuna.
Granada edged the encounter in every department but the lead given to them by Youssef El Arabi's 23rd-minute goal was being increasingly tested until the 79th minute, when Fernando Nano felled Yacine Brahimi in the penalty area.
Nano saw red and Guilherme Siqueira's cheeky dinked penalty wrapped up three vital points, before Diego Buonanotte added an exclamation mark late on.
The win sends Granada seven points clear of the relegation zone before 18th-placed Deportivo La Coruna face Espanyol on Sunday. If Depor fail to win that match, Granada will be safe.
Sunday's La Liga Preview
Barcelona take on Real Valladolid and need to win their remaining three games to bring up a century of points.
Despite the dominant nature of their title victory, it has been a season where Barca have slipped below their highest standards, but midfielder Xavi has urged the club not to make too many changes this summer.
Reflecting on his seventh league crown, the Spaniard told a press conference: "I could not have imagined winning so many titles. Our philosophy has yielded its rewards and I hope it continues to do so.
"We've set the bar very high and now it seems as though what we do falls short. We are competitive, we have to evaluate what we've done. It's not easy to win a title every season.
"I'm in favour of making few changes. It seems as though we're in a terrible situation and that we must change the whole team. But we're going through a good moment."
Malaga and Real Betis are in pole position to secure the remaining two places in the Europa League.
Malaga, whose finish to the season is being overshadowed by the future of boss Manuel Pellegrini, do not have a match this weekend while Betis travel to bottom side Real Mallorca, who could be relegated if they fail to win.
Second-bottom Celta Vigo also look very vulnerable having played a game more than their rivals while Deportivo La Coruna, in 18th, meet Espanyol.
Real Zaragoza, who sit two points above the bottom three, will hope to move away from trouble with victory over Athletic Bilbao, while the two teams above Zaragoza, Granada and Osasuna, play each other.
Saturday's La Liga Results
Sunday's La Liga Fixtures
Monday's La Liga Fixture
Mallorca vs Real Betis