Barcelona's hopes of claiming a record-equalling six trophies in 2015 look to be in tatters after they were thrashed 4-0 by brilliant Athletic Bilbao in the first leg of the Spanish Super Cup, with Aritz Aduriz netting a hat trick.
Barca made it four trophies from four on Tuesday night when they beat Sevilla 5-4 after extra time to win a thrilling UEFA Super Cup, but they were brought crashing back to earth at San Mames in stunning style on Friday night.
Mikel San Jose's breathtaking goal from inside the centre circle gave Athletic a half-time lead and then Aduriz scored three times in 15 second-half minutes to all but settle the Supercopa ahead of Monday's return leg at the Camp Nou.
Perhaps concerned about fatigue following his side's midweek efforts in Tbilisi, Georgia, Barca boss Luis Enrique made five changes to his starting lineup at San Mames with Pedro -- the Manchester United transfer target who scored the Super Cup winner after coming off the bench -- one of those being drafted in.
However, it was Athletic defender San Jose who stole all of the attention in the first half with a brilliant 40-yard strike to put the Basque side, who lost 3-1 to Barca in May's Copa del Rey final, ahead.
Barca keeper Marc-Andre ter Stegen came out of his area to meet a long punt forward by opposite number Gorka Iraizoz but the German's header went straight to San Jose who, from near the halfway line, brought the ball down before smashing his shot over Ter Stegen and into an empty net.
That was enough to give the hosts the lead at the break, although they were also indebted to a brilliant one-handed save from Iraizoz on the stroke of half-time to keep out Lionel Messi's free kick as it curled towards the top corner.
Treble-winners Barca, without Neymar again through illness, picked up where they left off after half-time with Pedro smashing a shot against the crossbar in the 50th minute before Messi drew another fine stop out of Iraizoz moments later.
With his side on top, Enrique went for the jugular by sending on Andres Iniesta for Rafinha, but the Spain star had only been on the pitch barely 60 seconds when Athletic made it 2-0.
Sabin Merino sent in a cross from the left and Aduriz climbed above Javier Mascherano to send a thumping header into the roof of the net.
Enrique responded by replacing Sergi Roberto with Ivan Rakitic, but the Croatia schemer could not stem the tide and Aduriz added his second in the 62nd minute when he controlled a pass from Markel Susaeta on his chest before swivelling to send a right-footed shot past Ter Stegen.
That made it 3-0 but Athletic were not done yet and Aduriz completd his hat trick in the 68th minute from the penalty spot after Dani Alves has penalised from climbing on San Jose inside the box.
That consigned Barca to their joint-heaviest defeat in over a decade and has left them needing little short of a miracle to keep alive their chances of matching the record-breaking "sextuple" won by Pep Guardiola's side in 2009.