Osasuna have shown their strength against one of the Copa del Rey powerhouses, defeating Athletic Bilbao 1-0 at home in their semi-final first leg.

Moroccan forward Ez Abde scored the winner in the 47th minute with a low left-footed shot from inside the area after a breakaway.

"We knew that we had to pay attention to their counter-attacks," Athletic midfielder Dani Garcia said.

"In the end, that's how they hurt us. We wanted to earn an advantage here, but it's not that bad a result. We have to look at it positively."

Athletic - the second-most successful club in the competition behind Barcelona - are making their fourth-straight semi-final appearance in the Copa.

The Basque club was runner-up in 2020 and 2021, and lost to Valencia in last season's semi-finals.

Osasuna are in the last four for the first time since reaching the final in 2005, when they lost to Real Betis.

"It's a small advantage but it gives us more confidence going into the second leg," Osasuna midfielder Jon Moncayola said.

"We know that the game there will be completely different, with the fans supporting them. Hopefully this advantage will be enough."

Athletic were coming off two straight losses in the Spanish league, while Osasuna won at Sevilla on Sunday to snap a four-game winless streak.

The second leg will take place in Bilbao next month.

Real Madrid host Barcelona on Thursday (Friday AEDT) in what shapes to be a blockbuster first match of the other semi-final.