Wednesday's 3-0 win at home to Elche moved Barca a point above Sevilla into third place in La Liga, five points behind Atletico Madrid, but with an extra game played, Ronald Koeman's side needs all three points
Barca coach Ronald Koeman said in his pre-game press conference that this game and Saturday's trip to Sevilla were vital for his side's title chances, and he made changes to try and keep his squad fresh
PSG striker Kylian Mbappe helped his side's supporters forget the absence of Neymar and Angel Di Maria with a hat-trick that left Barca needing to score four goals in the return leg to highlight the club's recent decline.
Barcelona on Wednesday night trailed 2-0 in the 88th minute before an own goal and a header from Jordi Alba saw them take the game to extra time, reports Xinhua news agency.
Real Sociedad had lost their previous 24 league visits to the Camp Nou, but may have thought their luck was about to change when Willian Jose opened the scoring as Portu crossed back into the Barca