Benat Turrientes fired Real Sociedad into a 1-0 Copa del Rey semifinal first leg lead at Basque rivals Athletic Bilbao on Wednesday.
American coach Pellegrino Matarazzo's La Real, unbeaten in nine games across all competitions since he took charge, impressed at Athletic's San Mames stadium and deserved their derby triumph.
On Thursday holders Barcelona visit Atletico Madrid in the first leg of the second semifinal.
Real Sociedad took a convincing step towards reaching the Seville final as they continued their run of fine form under New Jersey native Matarazzo.
"It's a good result to be able to play the second leg at home in front of our fans," Turrientes told Movistar.
"It's less of a lead than it could have been, but not a bad result to take into the second leg."
🔚 FULL-TIME!! First step taken. In three weeks, the return leg at Anoeta. 𝗔𝗨𝗣𝗔 𝗥𝗘𝗔𝗔𝗔𝗔𝗔𝗟!!! 💙💙💙 pic.twitter.com/DtJvsddgb5
— Real Sociedad 🇺🇸 🇬🇧 (@RealSociedadEN) February 11, 2026
Athletic, 24-time winners – more than any side other than Barcelona – have struggled for consistency this season and were second best in front of their disappointed fans in a typically intense derby clash.
La Real slowly inched up the pressure during the first half and had a strong appeal for a penalty turned down before halftime when Aymeric Laporte handled Duje Caleta-Car's header.
The visitors largely dominated after the interval and Pablo Marin struck the post from close range after Athletic goalkeeper Alex Padilla saved Mikel Oyarzabal's effort.
Lively Portuguese winger Goncalo Guedes fired wide before creating the only goal of the game in Bilbao.
Guedes was taken out by Padilla as he ran through but the referee played advantage as Turrientes fired the winger's pass, released just before the collision, into an empty net.
Spain winger Nico Williams had a shot blocked for Athletic at the other end but it was Real Sociedad creating more danger and looking more likely to score a second than concede a leveller.
"In the first half we were quite comfortable... and then in the second they were able to get at us," Athletic striker Inaki Williams admitted to Movistar.
"There's still the second leg to go, 1-0 is not too bad to come back from, we'll go for it."
The second leg takes place on March 4 at the Reale Arena.