Defending Copa del Rey champions FC Barcelona have been eliminated at the round of 16 stage following a 3-2 loss at the hands of Athletic Bilbao in extra-time.
Barca made three changes to the side that lost to Real Madrid in the Spanish Super Cup, as Luuk de Jong, Frankie de Jong and Ousmane Dembele made way for youngsters Abdessamad Ezzalzouli and Ferran Jutgla.
Bilbao had a dream start after Muniain gave them the lead within two minutes with a strike on the far side of the box after a low cross by Nico Williams.
However, Ferran Torres levelled matters for the Catalan giants in the 20th minute with a curling strike into the top corner after he was setup by Sergio Busquets in the box.
The sides remained level well into the second stanza, with Marcelino's men threatening and Inaki Williams came close to snatching the winner five minutes before time with a dipping strike that came off the bar.
Inigo Martinez eventually made it 2-1 for Athletic with a close-range tap-in after a flick by Alex Berenguer from Muniain's free-kick.
However, Pedri snatched the equaliser for Barca in stoppage time with a smashing strike from the edge of the box after a cross by Dani Alves.
Bilbao regain the lead in the first half of extra-time, with Muniain converting a penalty after Jordi Alba had handled the ball in the box.
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Ten-man Real Madrid needed extra-time to book a spot in the quarter-finals after rallying from behind to secure a 2-1 win over Elche at Estadio Manuel Martinez Valero.
Madrid rotated the side that defeated Athletic Bilbao in the Spanish Super Cup, as only Lucas Vazquez, David Alaba, Toni Kroos, Rodrygo and Vinicius Junior retained their places.
After a slow start, Los Blancos were gaining momentum in the closing phase of the first stanza, creating chances but they did not have the finishing touches.
There was still not much separating the sides in the second stanza and the match inevitably went to extra-time.
The early exchanges of the first period of extra-time were lively but Madrid were reduced to ten men in the 12th minute of extra-time after Marcelo was red-carded for denying Tete Morente a clear goal-scoring opportunity with a trip on the edge of the box.
Gonzalo Verdu eventually broke the deadlock for Elche from the resultant free-kick, although he smashed home the rebound after his initial strike came off the wall.
However, Carlo Ancelotti's men levelled matters early in the second period of extra-time after Dani Ceballos' strike took a deflection off teammate Isco and went to the back of the net.
Eden Hazard was the hero for Los Blancos as he netted the winner five minutes before time with a strike into a gaping net from a tight angle after rounding goalkeeper Axel Werner from Alaba's through ball, while Pere Milla got a second yellow card and was sent off for remonstrating with the referee.