So, how do you beat Barcelona? That is what every coach in world football wants to know.
How do you beat a team that have lost just twice in 35 games this season - and one of those defeats was in the second leg of a Copa del Rey match with a weakened line-up? The first team had taken Real Betis apart 5-0 in the first leg.
Barca have won 20 of their 23 league games, though they did drop points in a 1-1 draw at Sporting Gijon on Saturday. They have won four and drawn two of their Champions League games so far ahead of their last 16 first leg against Arsenal in London tonight. And they have progressed to the Spanish Cup final, where they will meet Real Madrid.
Only Hercules of Alicante have beaten Barca's strongest first XI this season thanks to a shock 2-0 victory at Camp Nou in the second game of the league season. To do so, they defended deep, challenged aggressively and kept Barca as narrow as possible in an attempt to frustrate them.
Then they tried to hit the Catalans on the break. It worked, twice, as Nelson Valdez netted a goal in each half. What makes that result even more bizarre is that it is still the only time Hercules have won away all season.
Many teams have tried to adopt Hercules's formula. It is almost the default tactic in containing Barca. Unfortunately for them, almost all fail.
Another option is to maintain a high defensive line and attack them. To do that a team needs possession.
It almost came off for a skilled Villarreal side in November who only lost 3-1. Real Madrid tried this two weeks later in the last el clasico. They were destroyed 5-0.
An in-form Espanyol side that had won all eight of their home games also tried this in the Catalan derby two months ago.
It made for a thrilling encounter as Barca struggled to find a way through before Barca's superior fitness told. Espanyol lost 5-1.
Almeria did have some success when aggressively man-marking Xavi and Andres Iniesta last season. They achieved a 2-2 draw, with Barca's midfielders complaining of "anti-football" afterwards. Other teams try to smother Lionel Messi, but he is prone to making them look foolish through his peerless brilliance.
An Inter Milan side famously "parked their bus" in front of the Barca goal in last season's Champions League semi-final. This was Jose Mourinho at his obstinate best.
His side were aggressive and caused distractions wherever possible to delay Barca's natural game. There was little of the Corinthian spirit in their tactics which barely saw the ball and their own forwards seldom leave their own half, but Inter progressed to the Champions League final.
Pep Guardiola, the Barcelona coach, has since conceded that it was a game of chess that he lost.
Such a heavy dependence on defence falls apart if Barca, as is usual, get a breakthrough.
Arsene Wenger, the Arsenal manager, can call on the experience of playing Barca twice last season. And he will have his captain, Barca fan Cesc Fabregas, fit this time.
Barca have found English Premier League teams difficult to overcome because they are more physical than most Spanish sides.
That should be to Arsenal's advantage, but they start as clear underdogs. And there is another factor that a team needs to beat Barca: luck. Arsenal will be hoping for lots of it.
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How do you beat Barca?
It is not something Arsene Wenger is likely to do, but asking Jose Mourinho for advice might help. Despite Real Madrid's 5-0 defeat in December, the Portuguese is an expert in the subject after Inter Milan's masterclass in playing without the ball at Camp Nou took them to last season's Champions League final. Yet as defensive discipline and rigorous tactical planning is not Arsenal's forte, their best hope may be that Theo Walcott's speed can trouble Barca like last season.
Richard Jolly English football correspondent
The popular joke answer: play them at basketball. There is an idea that because Barca are a diminutive team they can be towered into submission, or, more brutally, roughed up. Inter, who knocked them out last year, approached the task of protecting a 3-1 first-leg lead with some pugnacious challenges, targeting Sergio Busquets, their deepest midfielder. Holland tried the same against a Barca-dominated Spain team and held them for over 90 minutes in the World Cup final. Scoring first can also panic Barca, at least for a while.
Ian Hawkey European football correspondent
Study the "paradox" Inter Milan exploited to better Barcelona in the San Siro last April. Part of the Barca method is to unbalance opponents by pressing high up the pitch. What Jose Mourinho observed was the space left on the opposite side of the field. He looked to keep seven or eight men behind the ball, but to hit quick passes to the flanks and then forward when they had the chance and it worked.
Duncan Castles Premier League correspondent