Second division Mirandes caused an upset by knocking Deportivo La Coruna out of the King's Cup on Tuesday and Sevilla joined them in the quarter-finals after making light work of city rivals Real Betis.
Mirandes drew last week's last 16 first leg at their Estadio Municipal de Anduva in Miranda de Ebro and a Daniel Provencio double either side of an Abdon Prats strike in the return game secured a superb 3-0 win on the night and a 4-1 aggregate success.
"We knew it was a big game for us and were confident of getting a good result," said Provencio whose side reached the semi-finals in 2012 before falling to eventual runners-up Athletic Bilbao.
"It doesn't really matter who we get drawn against in the next round," the former Rayo Vallecano midfielder told Spanish television.
"We have our weapons and will fight for everything. Our priority is the league and the Cup is just a bonus."
Deportivo, hammered 5-0 at Real Madrid in La Liga at the weekend, were whistled by their own fans as they fell to a team who were in the fourth tier less than a decade ago and have never played in the top flight.
It was a huge blow for the Galician club who came from two goals down to draw 2-2 at Spanish and European champions Barcelona in La Liga last month and are ninth at the halfway stage of the campaign.
"They are a very good team, very intense, and they played very well," said Deportivo midfielder Alejandro Bergantinos.
"We just have to look at what went wrong and make sure it doesn’t happen in the league."
Sevilla put themselves in a strong position when they won 2-0 at Betis last week and a crushing 4-0 success in the return at the Sanchez Pizjuan sent the Europa League holders through 6-0 on aggregate.
The tie was effectively over when captain Jose Antonio Reyes struck after four minutes before defender Adil Rami was left unmarked at a 35th-minute corner and cracked the ball past Betis goalkeeper Antonio Adan to make it 2-0.
Forward Kevin Gameiro raced away to score in the 73rd minute moments after coming off the bench to replace Fernando Llorente and Gael Kakuta, another substitute, completed the scoring in the 89th minute.
Cup holders and record winners Barcelona look certain to go through as they lead neighbours Espanyol 4-1 ahead of Wednesday's return.
Atletico Madrid, the 2013 winners, and Rayo Vallecano are level at 1-1 after last week's first leg, with the return at the Calderon in the Spanish capital on Thursday.
Villarreal need to overturn a 3-2 deficit when they host Athletic Bilbao on Wednesday while Gary Neville's Valencia lead Granada 4-0 before Thursday's return in Andalusia.
Third tier Cadiz, who went through after Real Madrid were expelled for fielding an ineligible player, look certain to be eliminated on Wednesday after losing 3-0 at home to Celta Vigo in the first leg.
The quarter-finals will be played over two legs later this month, with the semi-finals at the start of February and the final on May 21.
Image: Action from the King's Cup Copa Del Rey match played between Deportivo and Mirandes on Tuesday