Real Sociedad are on track to reach the Copa del Rey final for the first time in 32 years after beating second division Mirandes 2-1 at home in Thursday's semifinal first leg.
Spain international Mikel Oyarzabal fired the home side into the lead in the ninth minute but Mirandes, who have knocked out three La Liga sides on their way to the last four, levelled in the 40th through Brazilian forward Matheus Rodrigues.
Sociedad's Norway midfielder Martin Odegaard lost the ball in the build-up to the equaliser but redeemed himself three minutes later by netting on the rebound to restore the lead.
The Basque side had more chances after the break but were kept at bay by keeper Limones, who gave the minnows hope for the second leg next month at their tiny Estadio Municipal de Anduva where they have beaten Celta Vigo, Sevilla and Villarreal this season.
"We created a lot chances and were hoping for a better result but we have to look on the positive side and try to finish the job at their ground," Oyarzabal told reporters.
Sociedad last won the Cup in 1987 and are bidding to reach the final for the first time since 1988.
They pulled off a stunning 4-3 away win over Real Madrid in the quarterfinals and their team bus was greeted on arrival at the stadium by thousands of supporters waving flags and scarves, some of whom lit blue flares.
Sociedad's local rivals Athletic Bilbao beat Granada 1-0 at home on Wednesday in the other semi-final, setting up the prospect of an all-Basque final in Seville on April 18.