Lewandowski, signed from Bayern Munich this summer, scored his first Barça goal in the opening minute of the game, only for Alexander Isak to equalize five minutes later.
With the scores level, France international Ousmane Dembélé appeared to catch Sociedad defender Aihen Muñoz in the face with his elbow.
Dembélé avoided a red card and, in a cruel twist of fate, scored Barcelona’s second goal of the game after a sumptuous backheel assist from substitute Ansu Fati.
Fati’s introduction in the second half proved even more important as the 19-year-old laid on a plate Lewandowski’s second goal of the evening, before grabbing his own goal to make it 4-1.
Lewandowski himself was full of praise for his new teammates after scoring his first two goals for the Catalan club.
“The first goal that I score for a new team always goes for my father, who’s watching from the sky,” he said after the game. “It was incredible, I’m very happy and proud of the team because, in the second half, we were playing really well and we scored four goals. Now, we go back to Barcelona and we’ll enjoy it for the next few days.”
He added: “The first game [against Rayo Vallecano] wasn’t good, everything was new. In the first few weeks, we have to get to know each other and each match will be better. There are a lot of youngsters who I get chemistry on the pitch with quickly.”
It was the tale of a 34-year-old veteran striker and a 19-year-old wonder kid.
After a stunted season-opener last week in its goalless draw with Rayo Vallecano, manager Xavi’s side began to show glimpses of what it could be on Sunday.
With a blend of experience brought from outside the club — Lewandowski and Christensen — and a whole host of academy graduates — Pedri, Gavi, Ansu Fati and Alejandro Balde — Xavi’s team has heaps of potential.
And from the opening minute at the Anoeta Stadium, it looked like it was coming together nicely, as 18-year-old left-back Balde streaked down the wing before crossing the ball for Lewandowski to slot home.
But Barça was pegged back just minutes later. Frankie de Jong was caught in possession before Isak was slipped in, the Swedish striker’s shot looping over Marc-André ter Stegen in goal.
And Barcelona could — and possibly should — have been down to 10 men when Dembélé appeared to elbow Muñoz in the face, but the video assistant referee chose not to review the incident and Dembélé escaped without even a yellow card.
After the halftime break, and after the introduction of Fati in the 63rd minute, the game swung into Barça’s favor.
Fati, who is coming back from a season lost due to knee injuries, used his pace and exuberance to dissect the Sociedad defense, finishing the game with two assists and a goal.
After the match, Xavi said he was “very satisfied” with the win.
“At times, we had to have more patience — sometimes, we are too impetuous because we play with very young players,” he said.
“But I am very satisfied, this victory shows that we’re on the right path; last week’s result was a bit of a blow and winning here strengthens us … We had to be brave after not winning last week and the bet came out well for us.”