Imanol Alguacil's Real Sociedad have thrilled in the league, sitting third, but were missing veteran playmaker David Silva and Mikel Merino through injury.

Xavi Hernandez, on his 43rd birthday, guided his team to a nervy victory, in search of more silverware.

Barcelona came out of the blocks quickly and Robert Lewandowski had an effort blocked after the electric Dembele found him.

Gavi fired wide and Frenkie de Jong deflected in another strike but from an offside position and the goal was disallowed.

At the other end Takefusa Kubo crashed a shot against the crossbar, as the game ebbed and flowed in entertaining fashion.

Barcelona fans frequently showed their ire towards referee Jesus Gil Manzano in the first half – he was the official who sent off Robert Lewandowski against Osasuna in November, resulting in a ban which the Pole is still serving in LaLiga.

However it was Real Sociedad midfielder Mendez who was sent off at Camp Nou, just before halftime.

The Spaniard lunged in on Sergio Busquets, catching his compatriot with his studs above the ankle.

Early in the second half Barcelona broke the deadlock when Jules Kounde slid Dembele in down the right wing and he drove into the box and lashed past Alex Remiro at the near post.

Real Sociedad, despite their numerical disadvantage, battled well and should have levelled when Sorloth fired over from only a couple of yards out.

The Norwegian striker had netted five goals in his previous six games and looked aghast at his miss.

Barcelona survived two late scares after Ter Stegen gave the ball away but then saved from Robert Navarro and produced another fine stop to deny Jon Ander Olasagasti.

Osasuna face Sevilla later on Wednesday while on Thursday Real Madrid host Atletico Madrid and Valencia welcome Athletic Club in the other quarterfinals.