Brothers Inaki and Nico Williams scored to help Athletic Bilbao secure a 3-0 semi-final win over Atletico Madrid on Thursday and a 4-0 aggregate victory that sent the Basque side into their third Copa de Rey final in the last five years.
Bilbao, who reached their 40th Spanish cup final, will bid to end a 40-year title drought in Seville on April 6, when they face Mallorca who beat Real Sociedad 5-4 on penalties on Tuesday.
Ernesto Valverde's Bilbao team punished the visitors with clinical counter-attacks, playing with the advantage of having won the first leg 1-0 in Madrid.
In need of a goal to stay alive and missing France forward Antoine Griezmann due to an ankle injury, it was mission impossible for Atletico against opponents who had not dropped a point at home since October.
Not even the pouring rain could spoil Athletic's showdown in Bilbao, where they were roared on by a raucous San Mames Stadium packed of 52,000 adoring fans, the highest attendance in the club's history.
The home side dominated from the start against a subdued Atletico, with the jet-heeled Williams brothers a constant menace.
They struck in the 13th minute when Nico burst up the left wing before crossing for his brother Inaki who unleashed a superb volley into the top corner.
Bilbao attacked again in the 42nd minute and Inaki Williams set up Nico for a simple close-range finish.
"Our connection is real and it's working very well, we understand each other," Nico Williams told TVE.
"I'm delighted, it's a dream to reach the final and to do it in front of our fans that were fantastic as always. Athletic can do it all and hopefully win the final."
Bilbao continued to dominate and Gorka Guruzeta wrapped up a 10th consecutive home win in all competitions for the Basque side from a rebound in the 61st minute.
It was another disappointing result for Diego Simeone's Atletico Madrid who have won only one of their last seven competitive games.
They are fourth in LaLiga on 52 points, 13 behind leaders Real Madrid, and will be under pressure when they host Serie A leaders Inter Milan after losing the first leg of their Champions League last-16 tie.
"The Champions League, it's a difficult, complicated competition that requires strength, but who knows...?," Simeone told TVE.
