The warning signs were there on Tuesday. Barcelona beat Sevilla 5-4 in a thrilling UEFA Super Cup clash in Tbilisi to take another step towards claiming the sextuple this year. But on Friday Barca let in four once again - and this time it didn't score any at all.

Whichever way you looked at it, this was a mess at San Mames for the treble winner. Luis Enrique's experimental side had holes in its armory all over the pitch.

In defense, the partnership of Thomas Vermaelen (who missed the entire 2014-15 Liga season through injury bar the final fixture) and the off-form Marc Bartra was completely out of sorts, while Jeremy Mathieu was left out of the squad altogether following his poor performance in Georgia.

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In the fullback positions, Adriano (in for the injured Jordi Alba) and Dani Alves both endured miserable evenings. The latter gave away a penalty for the fourth goal, was fortunate to avoid a red card and also at fault for two of the others, as he was beaten comfortably on the right for the second and played the ball back across his own area to Aritz Aduriz for the third. Aduriz became the first player since Diego Forlan in 2005 to score a hat trick against the Catalans - but Alves lent more than a helping hand on this occasion.

Marc-Andre ter Stegen was also guilty of a glaring error. The German goalkeeper had already caused unnecessary danger early on with a poor kick and his headed clearance after 13 minutes went straight to Mikel San Jose, whose audacious lob was reminiscent of Dejan Stankovic for Inter against Manuel Neuer (then at Schalke) back in 2011. It was a great goal, but Ter Stegen could and should have cleared to another part of the pitch.

But it was more than just the defense. A midfield trio of Javier Mascherano, Sergi Roberto and Rafinha was clearly second best and the introduction of Andres Iniesta and later Ivan Rakitic was unable to turn the tide as Barca looked tired following its Super Cup exertions on Tuesday. Indeed, Barca fans will wonder with some justification why the superb Sergi Samper was not given a chance in this one.

In attack, Neymar is still out with mumps and Lionel Messi was unable to influence the game as he usually does simply because he was starved of service. On Tuesday, he scored from two fantastic free kicks and came close here too with another set-piece strike just before halftime, while Pedro (whose future remains uncertain) rattled the crossbar early in the second half.

One goal was never going to be enough for Athletic, but four gives the Basque club a wonderful chance to win what would be a first trophy since its Liga and Copa double in 1984.

Ironically, the Rojiblancos only qualified for this fixture because Barca won it all in 2014-15, but the Catalans cannot live on past glories and this was quite a reality check for Luis Enrique's men. That's eight goals conceded now in their first two matches - the same number they shipped in their opening 13 games last season. In other words: eight goals let in by Aug. 14 this time, compared to Nov. 1 in 2014-15.

At home and in front of the Camp Nou crowd, Barca is capable of brilliance and overturned a 2-0 deficit by thrashing AC Milan in the Champions League in 2012-13. A 4-0 loss is much more difficult, however, and Athletic's morale will be sky high after its wonderful win on Friday.

Luis Enrique's men, meanwhile, will be playing their third fixture in six days and must somehow pick themselves up - and they will need to tighten things at the back as well because just one Athletic goal at Camp Nou will mean Barca will require six to prevail.

"It is not pretentious to think of a comeback," Luis Enrique said after the game. "It wasn't our best version and we were unlucky. But if any team can come back from this, it's Barcelona." And he added: "It would be easy to regret now, but that's football. I wouldn't change the lineup I chose."

Having won the treble last term, the Catalans have had their sights set on claiming all six trophies and they looked odds-on to achieve it after overcoming Sevilla on Tuesday, but those hopes hang in the balance before thoughts of a sixth title at the Club World Cup in December can even enter their heads.

So in the aftermath of what was the team's most damaging defeat since the 7-0 aggregate loss to Bayern Munich in 2012-13, Barca begins its inquest now. And following the nightmare in Bilbao on Friday, the dream of emulating Pep Guardiola's great side and the sextuple remains alive for the moment. But perhaps only until the return on Monday.

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