Barcelona will have a mountain to climb at the Camp Nou on Monday if they are to keep their hopes alive of a clean sweep of trophies in 2015 after Athletic Bilbao inflicted a stunning 4-0 defeat on the Catalans in the first leg of the Spanish Super Cup. Barcelona recorded a dramatic 5-4 extra-time win over Sevilla to claim the UEFA Super Cup in Tbilisi on Friday to claim their fourth piece of silverware in the calendar year. But just 72 hours later there was ample evidence both of the same defensive mishaps that blighted them in the Georgian capital as well as the mental and physical fatigue the encounter and traveling had taken on the squad so early in the season.

Still, that should take nothing away from what was a superb performance from an Athletic side that had more than enough fitness issues of its own, with several players absent through injury. Sharper both on and off the ball, Athletic took a spectacular 13th minute lead from Mikel San Jose’s wonder goal from just inside the Barcelona half. And, despite bringing on the likes of Andres Iniesta and Ivan Rakitic, things only got worse after the break for Luis Enrique’s men. Aritz Aduriz was the man to do the damage with a 15-minute hat-trick he is unlikely to ever forget. The powerful striker twice made a mockery of Barcelona’s defending on crosses, before sending the beleaguered Marc-Andre ter Stegen the wrong way from the penalty spot. Dani Alves was the man punished to give away the penalty and, indeed, the Brazilian was horribly at fault for all three second-half goals.

But there was far more wrong with Barcelona than just Alves’ hapless defensive offerings. With his squad having just two days to recover from their exertions against Sevilla, Enrique elected to make five changes to his lineup. Lionel Messi and Luis Suarez started, alongside the unsettled Pedro, up front, but behind them there was an unfamiliar look about a team that triumphed 3-1 against the same opposition in last season's Copa del Rey final. As well as the players that did come in failing to impress, those remaining in the XI from Tbilisi had precious little to offer.

Back at the Camp Nou and with some time to recover, Barcelona’s firepower means they can’t be written off from mounting a sensational comeback and moving one trophy away from a magical six in 2015. But Ernesto Valverde’s side have not only given their supporters at the San Mames a memorable evening and a taste of revenge for May’s convincing Copa del Rey defeat, but also an incredible opportunity to land just the club’s second ever Super Cup and first since 1984.

Athletic had already threatened when Javi Eraso forced ter Stegen to tip a shot from the angle wide of his near post, when they took the lead in stunning circumstances. Barcelona’s German goalkeeper will have wanted to have done far better when coming racing out of his penalty area than to head the ball straight into the middle of the field, yet surely he couldn’t have been expecting the quality of what came next. After taking a touch into his path, San Jose struck a flat, powerful drive from the center circle that left Ter Stegen helpless as it flew over his head and into the back of his net.

Neither the goal or Athletic’s lead was a fluke -- the visitors were comfortably getting the better of last season’s treble winners. The closest Barcelona could come to a response was when Messi attempted to add to his two free-kick goals in the UEFA Super Cup, but this time saw his dead-ball effort just kept out by Gorka Iraizoz.

There were briefly hopes of a fight back in the second half. Pedro, in the lineup because of Neymar’s continued absence with mumps and despite continued speculation over an exit from the club, got in behind the Athletic defense but saw his effort crash down off the crossbar. And from there Barcelona were simply blown away by the home side. First, in the 53rd minute, debutante Sabin Merino easily got the better of Alves down the left flank and put in a fine cross that saw Aduriz rise majestically to head it perfectly into the net.

Less than two minutes later the striker had his second. This time the cross came in from the right, but again Alves failed to cover himself in glory, turning the ball back across the danger zone where Aduriz took a composed touch before blasting into the net. With Barcelona stunned, Alves completed his hat-trick of blunders by bringing down San Jose from a corner to give Aduriz the opportunity to get his own, far more impressive, hat-trick.

Athletic Bilbao 4 - 0 Barcelona All Goals and... by ViralDailyTV