That was truly remarkable. The best team in the world getting an absolute pasting. Plenty for Luis Enrique to mull over ahead of the new La Liga season. But before that, he's got the second leg to worry about. Join us for live text commentary of that on Monday evening. Until then, adios!
Goodness me, I'm not sure I can remember a match quite like that. Gentle curtain-raiser? The curtains have been ripped clean off the walls by that Athletic performance. They'll have high hopes of improving on last season's seventh place after a display like that.
Well, that is the quite the marker laid down ahead of the Spanish football season. A huge statement by Athletic Bilbao. As for Barcelona, they have massive work to do after conceding four goals for the second game in a row.
Mikel San Jose, who started this madness, goes into the book. And that's it! Barcelona have been humiliated! What an extraordinary performance from Athletic Bilbao.
Into added time now. What a job by Ernesto Valverde's men. The San Mames is jumping in the pouring rain.
Gurpegui, who has a nose like a boxer who's been in one too many fights, picks up a yellow for a shirt tug on Iniesta. The kind of peccadillo he's built a career on.
Pedro looks forlorn on the bench. If he didn't want that Manchester United move before, I bet he does now.
More defensive reinforcement for Athletic Bilbao. Eneko Boveda trots on for Markel Susaeta. If Athletic can just stop Barca scoring an away goal in the next five minutes, they've surely got this won.
Tell you what, this can't be doing much for Barcelona's confidence ahead of the new La Liga season. They get their league campaign under way next Sunday. Their opponents? Athletic Bilbao. Right here at the San Mames. Tasty.
Javier Mascherano goes in the book for a ragged tackle on Susaeta. Mascherano holds one finger up, as if to indicate that it's his first foul. Sure it is, Javier, sure it is.
Last time Barcelona lost by four goals? April 2013, in the Champions League semi-final against Bayern Munich. That one felt pretty shocking, but surely this is an even bigger surprise?
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That one was against Barcelona as well. Bilbao lost 5-1 on aggregate...
Bilbao new boy Javier Eraso is off, replaced by veteran Carlos Gurpegui, who is 35 next week. He'll add defensive ballast in the closing stages.
Lionel Messi has had a quiet night tonight, and when he does get a rare glimpse of goal, Aymeric Laporte is there with a superb block.
It's Friday night in Bilbao. It's a national fiesta tomorrow. They're beating Barcelona 4-0. Quiet night then?
Sandro is on for Pedro for Barca. Bilbao's Markel Susaeta goes into the book for a late tackle.
Unbelievably, this is the second game in a row in which Barcelona have conceded four goals, after their 5-4 Uefa Super Cup win over Sevilla. They'll do well to win this one, even over two legs...
Late foot in by Jabier Etxeita, and that earns him a yellow card...
I think it's fair to say that we won't be seeing the central-defensive partnership of Thomas Vermaelen and Marc Bartra again. They've been woeful...
Aritz Aduriz steps up and nervelessly slots the ball into the bottom corner. He's taking home the match ball this evening. What an extraordinary scoreline.
Dani Alves drags his man down at the near post as a corner comes in, and that's a penalty!
Lekue is on for Sabin, who has had a magnificent game.
What do Athletic do now? Go for the kill? Or shut up shop and hold on to what they've got? The signs are that they can tear Barcelona apart here - Eraso wins a corner with a menacing run straight at the heart of the defence.
What a night in Bilbao! Barcelona aren't just on the ropes, they're on the canvas! Barcelona fail to deal with a cross into the box, the ball drops to Aritz Aduriz, and the striker swivels and dispatches a superb strike into the corner of the net. Dare I say it, but tie over?
No surprise, Luis Enrique withdraws another youngster: the largely anonymous Sergi Roberto is hooked, and Ivan Rakitic is on in his place. Can he make a difference?
Rain teeming down in Bilbao now. This is turning into a very uncomfortable assignment for Barcelona.
Just prior to that goal, Andres Iniesta replaced Rafinha for Barca. Luis Enrique is wheeling out the big guns.
What a crucial sixty seconds in this tie! Barely a minute after Iraizoz denied Messi with that superb save, Athletic go straight up the other end and score. It's great work by Sabin down the left, he leaves the defence trailing, stands up a superb cross and Artiz Aduriz absolutely monsters Javier Mascherano in the air and plants a superb header into the net. This may be a two-legger, but we very much have an upset on our hands.Copyright: AP
And again Barca go close! Luis Suarez scampers down the right and pulls the ball perfectly in to the path of Lionel Messi, whose shot is brilliantly tipped away from the bottom corner by Iraizoz.
And just seconds after he could have been traipsing off the pitch for an early bath, Pedro comes within an inch of levelling this tie. A bouncing ball causes confusion in the Bilbao defence, Pedro latches on to it, takes a good first touch and sends a rasping shot against the crossbar.
Goodness me, Pedro is walking a tightrope. He's already been booked, and he jumps for a header with Xabier Etxeita and sticks his arm right into the defender's face. He looks pleadingly at the referee, who keeps his cards in his pockets. Lucky, lucky boy.
No changes at the break, by the way. How long will Luis Enrique keep his powder dry?
We're under way in the second half.
Right then. Nearly ready for the second half. Should we expect a Barca backlash?
That Lionel Messi free kick, by the way, was Barcelona's first and only shot on target of that half. Not having it all their own way.
And that's the break. Athletic Bilbao lead the Treble winners, and they're good value for it too.
Magnificent stop! Lionel Messi coaxes an exquisite free kick up and over the wall, it looks certain to drop into the top corner, but Gorka Iraizoz covers an absolute acre to get across and push the ball over the top.
That's better from Barcelona. Pedro bursts threateningly through the heart of the Bilbao defence and Benat is forced to chop him down on the edge of the area. Free kick, prime Lionel Messi territory...Copyright: AFP/GETTY
Another man in the book. This time it's Bilbao's Javier Eraso for a cynical trip on Pedro.
Now that's what I call nonchalant. Barcelona whip in a dangerous cross from the right, but Benat, on the edge of his own box, has the sangfroid to direct a cushioned header back into the gloves of his keeper. Super-cool.
It's been coming. Pedro's frustrations get the better of him as he commits a niggly foul and then tosses the ball away petulantly. Out comes the yellow card for the first time in the match.
This is no meaningless pre-season trinket. Marc Bartra is absolutely cleaned out by a superbly timed crunching tackle from Aymeric Laporte. Play on, says the referee, quite rightly.
It's not quite happening for Lionel Messi at the moment. He picks the ball up on the edge of the area and looks to jink his way through the Athletic back line but the tackles are robust and the Argentine's way is blocked.Copyright: AP
Lionel Messi gets those scampering feet going for the first time, but youngster Sergi Roberto lets him down when he can't quite work the one-two with the little Argentine wizard. Barcelona haven't forced Iraizoz into a save yet.
There's a whiff of panic in the Barca defence at the moment, make no mistake. Sabin whips a terrific cross in from the left and Thomas Vermaelen can only manage to hoof it untidily behind for a corner.
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He's been quiet so far though...
Pedro's a lucky boy here. He slides in very late on Aymeric Laporte, to deafening whistles from the San Mames faithful, but the referee keeps his cards in his pockets. Athletic on top.
Ohh, what an opportunity that is. A great back-header springs Aritz Aduriz in behind, it's a two-on-two but his attempted through-ball can't locate Javier Eraso.
And then up the other end, Barca get their best chance! Luis Suarez draws Athletic keeper Gorka Iraizoz out of his net, dinks the ball up into the middle with the net unguarded, but Aymeric Laporte is on hand to head over the bar. Breathless stuff.
Well well. Penny for Luis Enrique's thoughts. He's gambled a bit with his starting line-up, leaving out trusted lieutenants like Iniesta, Pique and Rakitic, but he'll be sweating under his collar now that his team are behind. Will he be pondering half-time reinforcements already? His team look short of ideas.
Barcelona look shellshocked, but they win a corner when Pedro's attempted lay-off is deflected behind. It comes to nothing though, as Pedro's high boot gives Athletic a free kick and a chance to relieve the pressure.
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That is sensational. Mikel San Jose, take a bow. Barca keeper Marc-Andre Ter Stegen strides the edge of his area to head the ball clear, San Jose chests it down in the centre circle and unleashes an unstoppable dipping volley that soars over he head of the stranded German keeper and drops into the net. He could not have struck that any sweeter. What a start for the underdogs.
And with Vermaelen perhaps still temporarily discombobulated, Athletic get their first chance! New signing Javier Eraso gets in and sees his shot well beaten away at the near post by Marc-Andre Ter Stegen.
Yeesh. That's a nasty clash of heads between Thomas Vermaelen and Bilbao target man Aritz Aduriz. Thankfully, after a quick burst of the magic spray, the both look OK.
Barca get their first sniff of an opening as Rafinha plays in Luis Suarez right down the pipe, but the linesman raises his offside flag. Looked a good decision.
Thomas Vermaelen is making just his second appearance for Barcelona tonight after a nightmare start to his Nou Camp career. The former Arsenal man earns an early free kick as Bilbao struggle to assert themselves.
It's Barca who are very much in control of this one in the early stages, monopolising position in that familiar way. Bilbao holding firm in the early stages though.
We're under way at the San Mames. Barca playing in yellow and blue, Athletic in their traditional red and white stripes...
The teams are in the tunnel now. Not long to go...
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Now then, what of Barcelona's wantaway winger and reported Manchester United target Pedro?
He's in the starting line-up for tonight's game, despite Barcelona's technical secretary saying he wanted to leave.
Pedro himself denied that, but admitted his situation was "difficult" and he harboured "a lot of anger" over sitting on the bench.
Let it out, Pedro son. Buy a drumkit. Take up kickboxing. Or better still, bang a few goals in.
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What of tonight's opponents Bilbao? They're taking part in tonight's showpiece by virtue of having reached last season's Copa del Rey, where they lost 3-1 to Barcelona.
Always a solid proposition, the Basque outfit enjoyed another respectable campaign last season, finishing seventh in La Liga.
As ever, Los Leones will rely heavily on the nippy wing play of Iker Muniain, and the goals of Aritz Aduriz, top scorer for each of the last three seasons.
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They might have won the Treble last season, but that hasn't stopped Barca raiding the piggy bank, browsing the catalogues, and treating themselves to some shiny new football players.
Atletico midfield magician Arda Turan and Sevilla winger Aleix Vidal have both arrived, but they'll have to wait a bit longer to lace up their boots...until 1 January, to be precise. That's when Barcelona's Fifa transfer ban expires, allowing the duo to be registered as players.
The upshot of that is that, for the time being, Barcelona will look much the same as they did last season - minus the totemic figure of Xavi, who has left for a little pre-retirement sojourn in the sunny climes of Qatar.
Some interesting team news, with youngsters Marc Barta and Sergi Roberto, as well as former Arsenal centre-back Thomas Vermaelen, handed starts for Barca, with the likes of Iniesta and Rakitic on the bench.
Athletic Bilbao XI: Iraizoz, De Marcos, Balenziaga, Laporte, Etxeita, San Jose, Benat, Eraso, Susaeta, Aduriz, Sabin Merino.
Subs: Herrerin, Boveda, Lekue, Elustondo, Gurpegui, Aketxe, Kike Sola.
Barcelona XI: Ter Stegen, Alves, Pedro, Suarez, Messi, Rafinha, Mascherano, Bartra, Sergi Roberto, Adriano, Vermaelen.
Subs: Bravo, Pique, Rakitic, Sergio, A.Iniesta, Sandro, Munir.
Our European football expert Andy Brassell has been gazing into the tea leaves in an effort to predict who will win Europe's big leagues this season. And he's confident that Barcelona will successfully defend their title in Spain.
"After a turbulent few years at the Nou Camp, stability now reigns," he writes. "It's debatable, meanwhile, whether Real under Benitez will be as strong as last season, never mind better."
But do you agree? Will Barca sweep all before them? Can Real Madrid end their four-year title wait? Do you foresee a strong Copa del Rey challenge from the likes of Atletico or Sevilla?
Let us know your predictions for the Spanish football season via the usual channels: on Twitter at #bbcfootball, by text to 81111, or via the BBC Sport Facebook page.
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We're not even midway through August and Barca have already got a nice bit of tin on the mantelpiece. The Blaugrana got their season up and running last week with a pulsating victory in the Uefa Super Cup (not to be confused with the Spanish Super Cup), overcoming Spanish rivals Sevilla 5-4 after extra time.
Lionel Messi opened his account with a casual double before Pedro grabbed a late winner, but while the attack looked to be in good working order, the defence was leakier than a dodgy paddling pool, letting in four for the first time in Luis Enrique's reign.
After the match, Barca defender Javier Mascherano told reporters: "There is a lot to improve on." Ominous.
Hello and welcome to live text commentary of the Spanish Super Cup first leg between Barcelona and Athletic Bilbao!
It's a great chance to get a look at Luis Enrique's side before they begin their campaign to mount an unprecedented defence of last season's treble.
They will be heavy favourites to pick up the first silverware of the Spanish season - but Athletic Bilbao will be desperate to deny them and avenge last season's defeat to the Catalans in the Copa del Rey final.
It promises to be an intriguing match...and the first leg gets underway in a little under half an hour.
Missed Messi?Copyright: Reuters
Been pining over Pique?Copyright: Reuters
Ready to get your teeth into another football season?Copyright: Reuters
Well, the waiting is over. Spanish football is back.