Marcus Rashford came off the bench to score for Barcelona but the La Liga leaders lost an incident-packed game at Real Sociedad.
The England forward equalised with a 70th-minute header in San Sebastian – his eighth goal in all competitions since joining on loan from Manchester United – to cancel out Mikel Oyarzabal’s side-foot volley.
But Barcelona were on level terms for less than a minute before Goncalo Guedes scored what proved to be the winner.
In a pulsating game, Barca were awarded a penalty only for it to be overturned and had three goals disallowed, while Dani Olmo hit the post twice.
Fermin Lopez, Frenkie de Jong and Lamine Yamal all had goals ruled out for offside inside the opening half an hour before Sociedad captain Oyarzabal put the hosts ahead with a sumptuous finish in the 32nd minute.
There was plenty more drama to follow.
Barcelona thought they had won a penalty deep in first-half stoppage time when 18-year-old Lamine Yamal went down under a challenge by Igor Zubeldia.
The referee pointed to the spot before a VAR review resulted in the spot-kick being overturned because of another offside.
After Olmo hit the post in the 47th and 49th minutes, Barca substitute Robert Lewandowski had a header pushed on to the bar by goalkeeper Alex Remiro.
The visitors levelled when Rashford pounced seven minutes after coming on, before Sociedad went ahead again almost immediately through Guedes.
There was still time for Barca to hit the woodwork once more – with Jules Kounde’s 85th-minute header crashing against the bar.
Sociedad finished with 10 men when Carlos Soler was shown a straight red for a late challenge on Pedri in the 88th minute, but survived nine additional minutes to beat Barcelona at home for the second successive season.
Barca’s third league defeat of the campaign leaves them with 49 points from 20 games – a point clear of second-placed Real Madrid – while Sociedad have climbed up to eighth.
