Carlos de Lerma struck after just six minutes to put the hosts ahead against the Spanish champions, who left Neymar on the bench.
Despite missing injured trio Lionel Messi, Andres Iniesta and Xavi Hernandez, Barcelona then simply overwhelmed its third-division opponents with its sheer attacking talent.
Pedro Rodriguez scored either side of Cesc Fabregas' second-half volley, and substitute Jean Dongou marked his debut with a late goal as Barcelona snapped out of their first slump of the season.
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