Swedish striker Tobais Grahn got a consolation goal for Gimnastic late in the game before Barca's Gianluca Zambrotta ended their scoring spree in injury time.
Sevilla started the night in third place, two points in arrears of the leading two, but went down 1-0 at home to Villarreal, who secured fifth place.
Fabricio Fuentes' header after 50 minutes provided Villarreal with their eighth consecutive win and a guaranteed place in the UEFA Cup next season.
Real Zaragoza finished sixth and secured the other slot in the UEFA Cup.
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