Barcelona qualified for the Super Cup final on Sunday with a crushing victory in Saudi Arabia.
Barca scored four goals in 16 first-half minutes to beat Athletic and set up a showdown against either Real Madrid or Atletico Madrid.
Ferran Torres opened the scoring with Fermin Lopez, Roony Bardghji and Raphinha before the break.
Raphinha scored the fifth early in the second half to cap off a stunning performance.
Barcelona took the lead in the 22nd minute through Torres, accepting a clumsy pass that appeared to be a shot from Fermin, and his fine first touch allowed him to fire into the back of the net from seven yards out.
The score was 2-0 after half an hour when Raphinha reached the touchline and his low cross was brilliantly met by Fermin.
Fermin then completed a hat-trick of goal contributions when he passed again for Bardghji in the 34th minute, although it was a simple pass to the latter, who twisted and turned in the box before firing low into the net.
Barcelona were running rampant at this stage and they added a fourth through Raphinha when he burst into the box and blasted into the roof of the net.
The Brazilian scored his second goal in the 52nd minute as Bilbao failed to clear the ball in the penalty area and Raphinha fired home.
