Alvaro Gomez brilliantly volleyed the hosts in front to stun their La Liga visitors.

Barcelona levelled through Ferran Torres' cool finish just before the break.

Jules Kounde's 25-yard strike and Alejandro Balde's solo effort won the tie in the second half.

Hoping to bounce back from a painful thrashing by Real Madrid in the Spanish Super Cup final last Sunday in Saudi Arabia, boss Xavi made numerous changes.

He rested striker Robert Lewandowski and put youngster Marc Guiu in to lead the line, along with Joao Felix.

But, for large periods, Barca were frustrated by the side who had knocked Villarreal out in the previous round, in front of a capacity 6,000 home crowd.

Line-ups Unionistas Formation 4-4-222Gimenez4Mayor5Ruiz15Jimenez11Gomez20Tur16Gomez23Serrano17Rastrojo7Losada1Martinez 22GimenezBooked at 78mins 4Mayor 5Ruiz 15JimenezBooked at 43minsSubstituted forRojoat 60'minutes 11Gomez 20Tur 16GomezSubstituted forNespralat 60'minutes 23SerranoSubstituted forVillarat 45'minutes 17RastrojoSubstituted forIvaylov Stankovat 60'minutes 7LosadaSubstituted forTeijeiraat 79'minutes Substitutes 2Camus 3Rojo 6Villar 8Nespral 9Ivaylov Stankov 10Ramirez 13Cacharron 14Planas 21Teijeira 24de Bustos 25Lopez Barcelona Formation 4-3-313Pena Sotorres20Roberto23Kounde15Christensen3Balde21F de Jong18Romeu32Lopez7F Torres38Guiu14Joao Felix13Pena Sotorres 20Roberto 23Kounde 15ChristensenSubstituted forCubarsiat 45'minutesBooked at 70mins 3Balde 21F de Jong 18Romeu 32LopezSubstituted forPedriat 61'minutes 7F TorresSubstituted forRoque Ferreiraat 82'minutes 38GuiuBooked at 51minsSubstituted forLewandowskiat 61'minutes 14Joao FelixSubstituted forGundoganat 61'minutes Substitutes 8Pedri 9Lewandowski 19Roque Ferreira 22Gundogan 26Astralaga 30Casado 31Kochen 33Cubarsi 37Delgado 39Fort Referee: Francisco Jose Hernandez Maeso Attendance: 6,246 Match Stats.