Published: 2019-04-21 02:57:45 BdST
Barca lead the standings on 77 points after 33 games, comfortably clear of nearest challengers Atletico Madrid who won 1-0 at Eibar earlier in the day.
French centre back Lenglet scored his first league goal for the Catalans to break the deadlock against the stubborn visitors right at the end of the first half with a crashing header from Ousmane Dembele's corner.
Sociedad were rewarded for their intelligent display when forward Juanmi equalised in the 62nd minute, sliding in to meet an incisive pass from Mikel Merino and diverting it past Barca's Marc-Andre ter Stegen.
But Barca hit back almost immediately when Lionel Messi picked out Alba, who did his best impression of the Argentine by cutting in from the left wing and producing a magnificent curling finish into the top corner.
The Catalans will be crowned champions for the 26th time if they beat Alaves on Tuesday and Levante next Saturday. They could clinch the title as soon as Wednesday if they win against Alaves and Atletico lose to Valencia.