Celta Vigo took advantage of their breakaway chances in the second half to stun Real Madrid 2-1 at the Santiago Bernabéu in the first leg of the Copa del Rey quarter-finals.

It was the fifth win in a row for Celta and the second consecutive defeat for Real after a run of 40 games unbeaten in all competitions.

Iago Aspas scored off a counterattack in the 64th minute and set up Jonny Castro’s goal after another break in the 70th, which came one minute after Marcelo had equalised for the hosts.

Celta eliminated Atlético Madrid at this stage of last year’s tournament. Real lost by the same score at Sevilla in La Liga on Sunday to end their unbeaten sequence that stretched back to a Champions League game at Wolfsburg in April.

“I don’t know what happened, but once again we didn’t concentrate enough and didn’t get into the game,” Zinedine Zidane told reporters after his team lost two games in a row for the first time under his management. “It’s a bad moment but we have to get over it. We have a second leg to turn it around but today was a bad game.

“Losing is always a possibility but the way we started the game is what annoys me the most because you know if you let the other team play they can cause you problems and that’s what happened.”

Celta host Real next Wednesday in the second leg with Zidane’s side needing to win by at least two goals or with a 3-2 scoreline to advance to the semi-finals. Real have never overturned a 2-1 home defeat in any competition in a two-legged tie.

“You can never relax against Real Madrid no matter what result you get and the tie is by no means over,” the Celta coach, Eduardo Berizzo, said.

“We’re going to require a huge night in Vigo to go through. Real Madrid are always the favourites against any team, but we’re excited about advancing, this is a great moment for the team.”

Aspas opened the scoring after a great run by Theo Bongonda down the left. Marcelo tried to clear Bongonda’s cross with a backheel, but Aspas picked up the ball to score from near the penalty spot.

Marcelo equalised five minutes later with a volley from inside the area after the ball was partially cleared. But Aspas found Castro in between defenders and he scored with a shot from the edge of the box.

Alavés took a huge step towards the last four by winning 2-0 at second-division Alcorcon thanks to two goals in stoppage time by the forward Ibai Gómez. In other first-leg matches on Thursday, Barcelona play at Real Sociedad while Atlético host Eibar.