Madrid, Jan 19 : FC Barcelona reached the quarterfinals of the Copa del Rey on Thursday night, fighting back to wear down RFEF I (third tier) Unionistas de Salamanca 3-1. Xavi Hernandez's side had to come back from behind against the underdogs, before Ferran Torres, Jules Kounde and Alejandre Balde turned the game around against a rival that gave everything their legs could give. After seconds into the game, Unionistas had the first chance as Jorge Rastrajo carved open the Barca defense to set up Mario Losada, who fired wide with only Inaki Pena to beat, reports Xinhua. While Losada showed his frustration, Xavi looked furious at the weak defending from his side. Unionistas gave as good as they got in the first 15 minutes of end-to-end football. As the half progressed, Barca took control but were sluggish with the ball. Unionistas' central defenders cleared everything, and it was the home side who took the lead with a stunning goal. Juan Antonio Serrano found space on the left and sent over a deep cross for the onrushing Alvaro Gomez to volley past the helpless Pena. Pena then produced an acrobatic save to deny Rastrejo in the 43rd minute. Two minutes later, a Unionistas' corner was blocked and with their defenders committed forward, Ferran Torres received the ball in his own half, before sprinting forward and scoring with a low shot. The second half began at a slower pace, with Barca again controlling things, but without really creating chances. On the hour, Xavi brought on Lewandowski, Pedri and Ilkay Gundogan for Fermin Lopez, Guiu and Joao Felix. The changes changed the game, and after Lewandowski's tame shot was saved, Kounde put Barca ahead with a 25-meter shot as the defense backed off in the 68th minute. Balde then assured the win in the 73rd minute with an excellent individual goal, as he turned, ran at a tiring defense and fired into the roof of the net Athletic Bilbao, Celta, Mallorca, Sevilla, Real Sociedad and Girona had booked their quarterfinal places on Tuesday and Wednesday. /IANS