Iran Press/ Europe: Xavi's side led when Ansu Fati, just off the bench, shot into the bottom corner from the edge of the box - his first La Liga goal since 6 November after injury struggles.
Former Barca defender Marc Bartra headed Betis level moments later.
But four minutes into stoppage time Alba volleyed in Dani Alves' cross.
Barcelona players gave their Real Betis counterparts a guard of honor before kick-off following the hosts' recent Copa del Rey win over Valencia.
It was an entertaining game with Ronald Araujo's header tipped onto the bar by Betis keeper Rui Silva, and Betis' Guido Rodriguez striking the post.
Second-placed Barca are now 11 points clear of Betis, who are fifth, with three games to go. They were ninth when Xavi replaced Ronald Koeman in November.
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Dominant Barça cruise to easy win at Camp Nou
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