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Barcelona secured an unconvincing 3-1 win at third-tier Unionistas de Salamanca in the Copa del Rey on Thursday to reach the quarterfinals.

After Alvaro Gomez brilliantly volleyed the hosts in front, Barcelona clawed their way back to triumph with goals from Ferran Torres, Jules Kounde and Alejandro Balde.

The Catalans were thrashed by Real Madrid in the Spanish Super Cup final on Sunday and the bare minimum they needed was to progress from the Copa last 16 as doubts swirl around the club and coach Xavi Hernandez.

"Winning the Copa is an objective and after a difficult defeat, we had to react," Kounde told Movistar.

"In the end, you can talk about the coach, but we are the ones who play.

"We have to react and continue forward with intensity, that's what we're lacking this year, and to be more decisive."

Hoping to bounce back from the Super Cup defeat, Xavi shuffled his pack.

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

Guiu, 18, scored the winner for Barca against Athletic Bilbao in La Liga on his debut in October.

The hosts, at their packed 6,000 capacity Reina Sofia stadium, were fired up and dreaming of an upset.

Unionistas beat Villarreal in the last round on penalties.

They spurned a fine chance in the first minute with Mario Losada firing wide after running in on goal.

Guiu had a chance to break the deadlock but his lunging effort was shovelled over by Unionistas goalkeeper Ivan Martin.

When the hosts struck to shock Barcelona, it was in spectacular fashion. Juan Serrano crossed to the back post and the unmarked Gomez superbly hammered home on the volley.

Inaki Pena made a smart save at the near post to deny Jorge Rastrojo as the hosts nearly doubled their lead, moments before Barca snatched the equalizer.

Torres broke free on the counter, running through one-on-one from the halfway line, and kept his cool to slide a finish into the bottom corner.

Bolt from the blue

Xavi replaced Andreas Christensen, who was suffering some discomfort, with 16-year-old centre-back Pau Cubarsi at half-time.

The Catalan coach cut a frustrated figure on his touchline and beat the dugout in anger as his team struggled to impose themselves on the Salamanca side.

Kounde put Barcelona ahead with a bolt from the blue in the 69th minute, after being given too much time 25 yards out.

Balde made amends for his poor marking for the Unionistas goal by netting Barcelona's third, a superb solo strike.

The left-back roared into the area and lashed home from a tight angle to wrap up the win.

Pena was forced into a superb double save in the 90th minute as the hosts commendably refused to give up, roared on by their proud supporters.

"These fans deserve the best, so it's a shame (to go out)," said Unionistas goalscorer Gomez.

"I hit (the ball) with the inside of my boot and with my soul, I aimed it the best I could and I was lucky and it went in."

Later Thursday, Atletico Madrid host Real Madrid in the final Copa del Rey last-16 clash.

CD Unionistas de Salamanca CF

CD Unionistas de Salamanca CF

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