Despite neither side registering a shot in the first 15 minutes, both had golden opportunities to break the deadlock early on.
Shortly after kick-off, Sociedad celebrations were cut short when Sergio Gomez’s deflected effort was ruled out for an offside in the build-up, giving Barcelona the chance to land the first blow, only to see Pedri’s block loop onto the roof of the net after placing Alex Remiro under pressure to clear.
The visitors were looking positive, striking the crossbar through Orri Oskarsson, who should have done better when one-on-one but turned out to be comfortably offside anyway.
However, Los Txuri-urdin were soon on the back foot, as just moments after that chance, they were down to 10 men. A darting run from Dani Olmo left Sociedad exposed, persuading captain Elustondo to haul down the Barca man and leaving referee Alejandro Quintero Gonzalez with no choice.
Facing a depleted side for the first time in this season’s LaLiga campaign, Blaugrana opened the scoring seven minutes later when Lamine Yamal sat down a defender before laying off to Olmo, who swept to the back post for 23-year-old Gerard Martin to side-foot home his first goal in professional football.
By the half-hour mark, the hosts had a two-goal cushion thanks to another Olmo assist.
This one was far from intentional though, with the Spain international firing a shot from the edge of the box into the net via a combination of Marc Casado – who also claims his first goal for Barcelona – and the left post.
The away side had a mountain to climb and were offering precious little as Pedri rifled a shot from range onto the frame of the goal following the restart.
If the contest wasn’t already over, two goals in the space of five second-half minutes confirmed the result.
Ronald Araujo was first to react when Robert Lewandowski’s header from a corner was parried, and having netted his first league goal of the season, the defender turned provider as his long-range strike was diverted past Remiro by the Polish international.
Lewandowski missed the opportunity to bag his brace with a mistimed header in the closing stages, but that ultimately proved academic with the victory secure.
Now unbeaten in 15 games in all competitions (W12, D3), Hansi Flick’s Barcelona move above Atletico Madrid to the top of the LaLiga standings, one point clear of Los Colchoneros and three above Real Madrid in third.
A tough afternoon for Sociedad ends with a perhaps predictable defeat – their 26th in 27 league H2Hs away from home – leaving Imanol Alguacil’s side ninth in a congested midtable.