WATCH: Barcelona stunned! Third-tier side Unionistas de Salamanca score with a thunderous volley in Copa del Rey last-16 clash to shock manager Xavi

Barcelona visited the Primera Federacion team in the round of 16 clash on Thursday. The minnows pulled off a shock just after the half-hour mark when Juan Serrano's cross fell to an unmarked Alvaro Gomez at the back post and he smashed beyond goalkeeper Inaki Pena.

Unionistas are the lowest-ranked team in the competition at the last-16 stage. Only one other team - Segunda Division side Tenerife - is not in La Liga. It was a momentous occasion for the club to take the lead against Xavi's La Liga champions, but the Catalan giants fought back and pulled level through a Ferran Torres goal just before half-time.

Barca coach Xavi will hope his team can get on top in the second half of the clash in Salamanca. The former midfielder is under pressure as his side have dropped to fourth in La Liga and sit eight points behind leaders Girona.