Barcelona's defensive frailties were once again evident as the treble winners were humiliatingly thrashed 4-0 by Athletic Bilbao in the first leg of the Supercopa de Espana on Friday, Aritz Aduriz netting a hat-trick.
Luis Enrique's men surrendered a three-goal lead against Sevilla in the UEFA Super Cup earlier this week before eventually winning 5-4 in extra-time, but Barca were not afforded such a dramatic escape this time around as Athletic took them apart.
Seemingly sensing Barca's jadedness from Tuesday's 120-minute ordeal, Athletic were sharp in the tackle and far quicker to the ball and, although the nature of the opening goal was by no means expected, the home side deserved to open the scoring 13 minutes in.
Mikel San Jose made the most of Marc-Andre ter Stegen's reckless dart out of his area to head clear, finding the net from 45 yards to leave the German looking stunned.
Barca appeared to produce as improvement at the start of the second half, with Tuesday's match-winner Pedro striking the crossbar, but Athletic doubled their tally almost straightaway – Aduriz heading past Ter Stegen.
Aduriz slammed home his second just after the hour mark and then rounded off a fine individual display 22 minutes from the end, sliding home a penalty to embarrass Barca and take a huge advantage into next Monday's second leg.
Despite what ultimately proved to be a disastrous day in Bilbao, Barca began the contest in typical fashion, dominating possession and getting the ball forward quickly as the European champions probed for an early breakthrough.
But, with Thomas Vermaelen starting in place of the rested Gerard Pique, Barca looked frail at the back and Ter Stegen was forced into an important stop to deny Aduriz at the near post in the 11th minute.
And just two minutes later Athletic were in front, as Ter Stegen's headed clearance from outside the area was pounced upon by San Jose just inside the Barca half and the defender smashed a flawless half-volley over the stranded goalkeeper from the centre circle.
There was no sign of that freak opener jolting Barca into life, though.
In fact, the hosts looked more likely to double their advantage and a crucial Marc Bartra tackle halted Javier Eraso nine minutes before the break, with the midfielder all set to pull the trigger in the area.
Athletic had Gorka Iraizoz to thank for ensuring their lead remained intact at the break, however, as the goalkeeper produced a wonderful flying save to tip Lionel Messi's goal-bound free-kick over.
Seemingly following a half-time dressing down from coach Luis Enrique, Barca came back out after the break with a renewed sense of urgency and should have equalised four minutes in, but Pedro's fierce drive came back off the frame of the goal.
Athletic's response was swift and devastating.
Just three minutes later, Sabin seized on a Sergi Roberto error and delivered a fine cross from the left, with Aduriz rising above Javier Mascherano to net with a trademark towering header.
Aduriz was again in the right place at the right time in the 62nd minute, as he collected Eraso's squared pass and found the bottom-left corner.
A moment of rashness from Dani Alves saw the Brazilian concede a penalty six minutes later as he bundled into his man at the back post, and Aduriz took full advantage from the spot-kick, coolly stroking past Ter Stegen.
Barca looked incapable of mounting much of a response to the onslaught and Athletic cruised to memorable victory, going some way to erasing the pain of May's 3-1 Copa del Rey final defeat to Luis Enrique's men.
