Pablo Ibanez's superb volley helped Osasuna stun Athletic Bilbao in extra-time to reach the Copa del Rey final with a 1-1 draw on Tuesday, progressing 2-1 on aggregate.

Athletic dominated throughout and only a sensational display from Osasuna goalkeeper Sergio Herrera and profligate finishing forced the match to extra-time.

Inaki Williams struck in the 33rd minute to cancel out Ez Abde's first-leg strike for Osasuna, but Athletic could not find a winner, and Ibanez stroked home from the edge of the box with four minutes remaining to shock San Mames.

Ibanez's effort helped Osasuna reach the Copa del Rey final for the first time in 18 years, and only for the second time in their history, with the club yet to lift the trophy.

Jagoba Arrasate's side beat Real Betis and Sevilla on their spectacular cup run and will face either record winners Barcelona or Spanish and European champions Real Madrid in the final on May 6.

"Right now, I have no words, we were suffering like dogs all through the game," Ibanez told Movistar.

"(This goal) is for all those fans up there shouting, it's something that can't be explained.

"We knew that it could happen, that they could score against us. We suffered, we kept working and in the end we got our reward.

"Now that we are here we have to dream and go for it. I don't care if it's Madrid or Barca, we'll keep dreaming."

Both of their previous cup games went to extra-time, along with their round of 32 clash with Gimnastic, in which Ibanez was sent off.

Athletic have reached the semi-finals four seasons in a row, but have not lifted the trophy since 1984. They have lost six finals since their last triumph.

"We had so many chances for the result to go our way, but in football sometimes these things happen," said Inaki Williams.

"We're very sad, messed up, we will try and pick our heads up and come back."

Athletic coach Ernesto Valverde selected Iker Muniain in attacking midfield, with Oihan Sancet deployed slightly deeper, instead of Dani Garcia, as the hosts sought to turn the tie around.

The game kicked off with a 10-minute delay after Osasuna's coach was held outside the stadium for over half an hour because of overcrowding.

Backed by their vociferous fans, Athletic started well and Herrera denied Gorka Guruzeta.

Nico Williams dragged a shot narrowly wide of the near post after 25 minutes as Valverde's side continued to push, with Herrera parrying Oscar de Marcos's header.

Eventually Inaki Williams opened the scoring after 33 minutes, staying onside to cleverly divert home Mikel Vesga's header from point-blank range.

It was his first goal since October for Athletic, ending a run of 18 matches without scoring, statistically his worst ever stretch at the club.

The Ghana striker converted again shortly before the break, but this time he was offside as he stretched to reach his brother Nico's cross.

With 20 minutes remaining Inaki fed Nico, who should have scored at the end of an electric break, but fired over the bar leaving Athletic fans howling.

The Basque side set a record home attendance of over 51,500, and they were left frustrated again when Herrera saved well from Inigo Martinez at his near post.

That feeling only grew as Herrera denied Raul Garcia and Nico Williams slashed the rebound high into the stands with the goal gaping.

Osasuna clung on for extra-time, with their backs to the wall and reliant on their goalkeeper.

Chimy Avila fired over for the visitors on a rare foray forward near the end of the first period of extra-time. If it was a warning, it was not heeded.

With the game heading for penalties, Jon Moncayola crossed and Ibanez took on a first-time volley which flew into the top corner and earned Osasuna a historic victory.

It was their first goal since Abde's first-leg strike on March 1.

Barcelona host Real Madrid in the second semi-final on Wednesday, holding a 1-0 lead.