Fernando Llorente's dramatic late goal secured Athletic Bilbao's place in an all-Spanish Europa League final against Atletico Madrid after they beat Sporting Lisbon.
Atletico Madrid comfortably held on to a first-leg lead to beat La Liga rivals Valencia on Thursday.
A 3-1 success for Bilbao, chasing their first European title, means it will be an all Spanish affair against Atletico, who won 1-0 on the night, in the May 9 showpiece in Bucharest.
Llorente was the hero as he set up Bilbao's first two goals and then pounced at the near post with an opportune finish to volley the crucial strike two minutes from time that took the Basques through 4-3 on aggregate.
"This is incredible," said Llorente said in a television interview, struggling to make himself heard over the fans
celebrating wildly in the stands.
Nicknamed the Lion King, his contribution helped Bilbao who beat Manchester United in the last 16, reach their second final in major European football after their last appearance in 1977 ended in a defeat by Juventus.
Marcelo Bielsa's side grabbed the opening goal on Thursday when Llorente cleverly chested a cross into the path of Markel Susaeta who volleyed past Rui Patricio from close range.
Both sides drove forward at every opportunity and both had chances before Sporting pulled level on the night in the 44th minute when the ball fell to Dutch striker van Wolfswinkel on the edge of the penalty area and he fired low into the corner.
Sporting's aggregate lead lasted a mere two minutes before Llorente got his second assist when he set Ibai Gomez clear to finish with a shot into the far corner in first half added time.
The second period followed a similar pattern to the first, Bilbao's Javi Martinez heading against a post from a corner and Emiliano Insua also striking the frame of the goal with a powerful deflected low drive for Sporting.
With extra time looming, Llorente nipped in front of his marker and diverted a Gomez centre in off the post to send the
home fans into raptures.
Atletico Madrid won last week's semi-final first leg at their Calderon stadium 4-2 and when Adrian powered home a stunning goal from wide on the right on the hour, as Valencia's hopes of turning the tie around were crushed.
Diego Simeone's side had midfielder Tiago sent off in the 79th minute after players from both sides became involved in an ugly melee and the Portuguese slapped Valencia striker Roberto Soldado across the face to earn a straight red card.
It all came too late for the home side and Atletico cruised to their 11th straight win in Europe this season as they claimed a 5-2 aggregate success.
"We knew it would be difficult and they pressured us well, which is to be expected here at the Mestalla," said Simeone.
The last time two Spanish teams contested the final of the competition formerly known as the UEFA Cup was in 2007, when Sevilla beat Espanyol on penalties after a 2-2 draw.
Bilbao were the only side in the last four never to have won a European trophy, while Atletico were Europa League winners in 2010, beating English side Fulham 2-1.