Alex Berenguer earned Athletic Bilbao an impressive 1-0 win at Atletico Madrid in a tense Copa del Rey semi-final first leg clash on Wednesday.
The winger rolled home a 25th minute penalty to secure the victory but Atletico were frustrated after a late spot kick in their favour was anulled.
Yeray Alvarez felled Alvaro Morata in the area in stoppage time but a VAR review showed the forward was offside in the build up.
Athletic inflicted Atletico's first home defeat of the season across all competitions.
"They pressed us well in the second half especially, but in the end we got a very good result," Berenguer told Movistar.
"We did what we've been doing all the year, the team sacrificed a lot and this is the way we have to continue."
Sitting fourth in La Liga and 10 points adrift of leaders Real Madrid, cup success remains Atletico's best avenue to silverware this season.
Diego Simeone's side defeated current holders Real Madrid in the last 16 and scraped past Sevilla to reach the semis, but will need to mount a comeback in the Basque Country.
Athletic, meanwhile, ousted record 31-time winners Barcelona in the quarter-finals and played with grit and determination at the Metropolitano stadium.
The Basque side have lost the last six Copa finals they have played in, although with 23 triumphs have won more than any side except Barcelona.
The visitors took the lead in the capital when Reinildo Mandava clumsily ploughed into Benat Prados to concede a penalty and Berenguer sent Atletico goalkeeper Jan Oblak the wrong way from the spot.
Memphis Depay might have levelled but Aitor Paredes was alert to block his shot after a Julen Agirrezabala error, while Antoine Griezmann fired narrowly wide.
Samuel Lino whisked a low effort past the post early in the second half as Atletico sought a leveller.
Asier Villalibre should have doubled Athletic's lead but lashed into the side netting after Oblak parried a shot invitingly into his path.
Regardless, Ernesto Valverde's side take an impressive result back to their San Mames fortress for the second leg on February 29.
Atletico almost snatched an equaliser but Inigo Lekue hacked an Angel Correa effort off the line in the final stages.
In stoppage time Atletico thought they had a penalty of their own but Morata's offside saw it cancelled and the striker headed inches wide with the last touch of the game.
Real Sociedad drew 0-0 at Real Mallorca in the first leg of the other semi-final on Tuesday.
