Athletic Club came from behind to beat Atletico Madrid 2-1 and set up a Spanish Supercopa final against Real Madrid on Sunday.
All the games came in the second half, with Nico Williams scoring a dramatic winner in the 81st minute just four minutes after Yeray Alvarez had equalised.
Atletico had taken a 62nd-minute lead when Joao Felix's header hit the post and then rebounded into the goal off of goalkeeper Unai Simon's back.
However, there was to be no Madrid derby in this weekend's final as Athletic fought back to set up a meeting with Real, who beat Barcelona on Wednesday.
Atletico ended the game with 10 men after Jose Maria Gimenez's dangerously high foot in the fourth minute of stoppage saw him sent off.