Dembele, who was brilliant on the night, fired home in the 52nd minute, beating goalkeeper Alex Remiro at his near post after latching on to a through ball from Jules Kounde.
Barca will regret not taking their chances to kill off the game, with Gavi hitting the woodwork, and they had goalkeeper Marc-Andre ter Stegen to thank for late stops from Robert Navarro and Jon Ander Olasagasti.
1. Barcelona's Gala XI arrives, does just enough
The best periods in Barcelona's recent history have often been accompanied by a clearly defined "Gala XI" -- the term given by the local media to the first-choice team. Under Xavi, the Gala XI has not always been obvious, but it does appear to be now.
Against La Real, the Barca coach lined up with the same side which easily beat Real Madrid to win the Spanish Supercopa recently: Ter Stegen in goal, a back four of Kounde, Ronald Araujo, Andreas Christensen and Alejandro Balde; a midfield of Busquets, Frenkie de Jong, Pedri and Gavi; and a front line of Dembele and Robert Lewandowski.
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The first 30 minutes here were brilliant, even if there were no goals. The football was good, there was an offside goal and missed chances from Kounde, De Jong and Dembele. On another day, Barca would have scored two against an in-form opponent who came to Camp Nou on a nine-game winning run.
Mendez's red card only upped Barca's domination and they eventually broke the deadlock early in the second half. What followed was not so good. Barca failed to score a second goal and in the end were hanging on, with Sorloth missing a sitter and Ter Stegen making two big late saves.
2. Dembele living up to Xavi's praise with game-winner
Xavi has repeated throughout his time as Barca coach that, well coached and performing consistently, Dembele can be one of the best players in the world. The Frenchman is now regularly producing match winning performances.
Wednesday's performance was not just about his goal. It was everything. It was his searing pace. It was his decision making. It was his chance creation. Real Sociedad could not stop him. He was unplayable. His goal was excellently took and he also set up openings for De Jong and Gavi, the latter hitting the bar.
3. Mendez red costs La Real their winning run
Real Sociedad have been one of the best teams in Spain this season, but Mendez's dismissal ended any hopes they had of extending their winning run in all competitions to 10 games. They had just about weathered the Barca storm in the first half when the midfielder was sent off.
Already without the injured David Silva and Mikel Merino, dropping down to 10 men made a difficult task at Camp Nou a near impossible one. That said, even with a man less, they came close to equalising through Sorloth, who won't want to see a replay of his miss from six yards, before substitutes Navarro and Olasagasti brought the best out of Ter Stegen.
La Real now turn their attention back to LaLiga. They travel to Real Madrid on Sunday and can move level with Carlo Ancelotti's side with a win at the Santiago Bernabeu. They also remain in the Europa League.
Best and worst performers
BEST: Ousmane Dembele, Barcelona
At the heart of almost everything Barca did with a blistering performance.
BEST: Jules Kounde, Barcelona
After Dembele, a handful of Barca players impressed, but Kounde's contribution in defence and attack -- setting up the goal and almost scoring himself -- stood out.
BEST: Take Kubo, Real Sociedad
The away side's brightest player, hitting the bar in the first half and causing problems with his pace and close control in the second.
WORST: Brais Mendez, Real Sociedad
Could have no complaints about his first-half red card for an over-the-top challenge on Busquets.
WORST: Alexander Sorloth, Real Sociedad
The Norway striker produced a candidate for miss of the season, turning over the bar from six yards out with the goal gaping.
WORST: Robert Lewandowski, Barcelona
A rare off night for the Poland international, who already has 22 goals for Barca this season.
Highlights and notable moments
Ousmane Dembele is having a stellar year because of plays and goals like these.
DEMBELE WHAT A HIT! 🚀🚀🚀 pic.twitter.com/ivFYy0ZsVU— ESPN FC (@ESPNFC) January 25, 2023
Even with 10 men, Real Sociedad were in it all the way until the final whistle, keeping Barcelona keeper Marc Andre Ter Stegen on his toes.
Ter Stegen cleans up his own mess pic.twitter.com/fYareNysyy— ESPN FC (@ESPNFC) January 25, 2023
A game-saving effort by the German there after an initial blunder.
After the match: What the managers and players said
Barcelona manager Xavi Hernandez, on Ousmane Dembele's performance: "I think he has matured a lot since we took over. We have given him the tools. He is lethal. We always say when he comes inside, he has to shoot more because he has the quality and can make the difference in games. You see the faces of the full-backs, they suffer. We have just given him confidence. He has so much potential. I believe in him. I think a lot of this comes down to making the right decisions. He is also enjoying himself and the fans are enjoying him. I am delighted for him because he is a good guy and good professional. He has turned things around and that is not easy at Barca."
Xavi, on coaching Dembele: "He's the one full of confidence and quality. We try to guide him. I think he is happy and that is important. I speak often with him. For me, he is still one of the best in the world in his position. He has so much quality but from there you have to believe in yourself. At Barca, it's important to have that mentality to believe that you can influence games."
Real Sociedad manager Imanol Alguacil, on the result: "We are annoyed because we wanted to get through. It's difficult here 11 vs. 11 against Barca in their current form, so imagine ... But we knew we would get chances. We were close, even with a man less.
"I don't usually like the word proud because it means you have lost, and we came to win. The red card marks the game. We competed, we had chances to draw. But against Barca, in their form, with a player like Dembele, it is complicated. In the last 10 minutes they seemed more nervous and 1-1 seemed more likely than 2-2. It still hurts, I am annoyed."
Alguacil, on Mendez's red card: "If I am the referee and I am called to look at the image, I do the same. But it's football, and I am sure Xavi would agree with me that without VAR, it passes as just another moment."
Key stats (provided by ESPN Stats & Information)
- Barcelona has won six of the seven games that Ousmane Dembele has scored in this season, with the lone exception being the Champions League group-stage match vs. Inter Milan (3-3 draw).
- Barcelona extended a club-record home winning streak vs. Real Sociedad, now up to 27 games.
Barcelona: The top side in LaLiga return to action with a trip to Girona on Saturday. Three more league games (Real Betis, Sevilla, Villarreal) before the Europa League campaign returns with a first-leg matchup against Manchester United (Feb. 16) at Camp Nou.
Real Sociedad: Another measuring stick test for the San Sebastian side. This time a trip to Real Madrid in a Sunday clash of the second- and third-placed teams in LaLiga.