Alexander Isak, 20, has scored against Espanyol and Celta Vigo away this season.
The striker's third La Liga goal came against Barcelona himself in front of the home fan at the Reale Arena in the Basque Country.
Real Sociedad was 2-1 down in the 60th minute when the Swede struck a goal-keeper return from German Marc-André ter Stegen.
A while later, the Swede was exchanged for standing ovations by the home crowd.
It stands 2-2 and the match is ongoing