Copa del Rey holders leaders Atletico Madrid edged towards a possible semi-final meeting with neighbours Real Madrid with 1-0 win over Athletic Bilbao in their quarter-final, first leg at the Vicente Calderon on Thursday.
Uruguayan defender Diego Godin powered home the only goal of the game four minutes before half-time as he rose highest to meet Koke's cross from the right.
The hosts also had the better of the chances after the break, but failed to force Iago Herrerin into a serious save as they had to settle for a slender lead to take to Bilbao for the second leg next Wednesday.
"We had chances to kill the tie off and add to our advantage, but we are satisfied with how we played," Koke told Spanish TV station Canal Plus.
"We take a goal advantage to San Mames which is important.
"We are on a tough run of games against opponents with great quality and we have to value this victory because we were up against a very good side."
Both managers named strong sides for what was expected to be the most keenly contested of the quarter-final ties and so it proved in a game of limited opportunities.
Adrian Lopez had the first clear-cut opening of the game when he fired into Herrerin's legs five minutes before the break.
However, Diego Simeone's men only had to wait 60 seconds more to open the scoring as Koke's wicked cross got the thunderous finish it deserved from Godin.
Atletico also ended the second period with a flourish, but couldn't find the vital second goal as after Herrerin had smothered Raul Garcia's tame header, Toby Alderweireld volleyed wide another fine Koke cross in stoppage time.
Real Madrid already look well set for the last four after winning their quarter-final, first leg 1-0 away at Espanyol on Tuesday.
Meanwhile, on the other side of the draw, Barcelona and Real Sociedad are likely to meet in the semi-finals after comfortable victories over Levante and Racing Santander respectively on Wednesday.