Diego Martinez's side have impressed so far in 2019-20, following their return to the Spanish top flight and they stunned Ernesto Valverde with a 2-0 victory at the Nuevo Estadio de Los Carmenes.
Ramon Azeez stunned the visitors with a goal inside the first 60 seconds, heading home at the far post, after Jose Puentas profited from a slip by Junior Firpo - on his first start for the Catalan side.
The visitors never really recovered from that early setback, with Luis Suàrez and Antoine Griezmann unable to trouble home defence.
Valverde brought on Lionel Messi and Ansu Fati at half time, but again they struggled to make any attacking inroads as the hosts looked to preserve their lead.
Any chance of a late FC Barcelona comeback was killed off with 25 minutes to go as substitute Arturo Vidal conceded a penalty, and Alvaro Vadillo scored from the spot.