Across four seasons of elite European football, Barcelona and Manchester United have been the game's dominant forces. Each has reached three Champions League finals. Each has lifted the trophy once. Only Jose Mourinho's tactically and psychologically inspired Inter Milan side has interrupted their joint dominance.
As the pair prepare to contest European pre-eminence, consensus has it that Barcelona, with Lionel Messi establishing his status as a great, are a stronger unit than the one that defeated United in the 2009 final. The same analysis has Sir Alex Ferguson's team, shorn of Cristiano Ronaldo, weaker than two summers ago.
How, then, can United win? Here are two obstacles they must overcome to have a chance.
Ÿ The possession problem. Barcelona hold the ball better than any team in the modern era. They use possession defensively - to tire opponents and hold them away from goal - and as the platform for their attacking. Possession is the team's identity, their philosophy, and their greatest quality. In this season's Champions League they have had an average of 62 per cent possession; close to two thirds of a match.
Attempting to win the ball by constantly encircling Barca's passers has proven a reckless method. Ferguson had his team press high up the field in the 2009 final. United started impressively but conceded to Samuel Eto'o on a counter and never recovered.
Pressing Barca close to their own goal is both a poor-odds gamble on scoring first, and physically impossible to sustain for 90 minutes. It also leaves space for the Spanish champions to exploit the speed of Dani Alves and their three forwards. Attempting to play the type of open game United use to bowl over average Premier League opponents would be equally dangerous, defensively. With Barca naturally gathering the majority of possession, United would mentally and physically tire chasing them.
Ÿ The Messi problem. Nominally the central forward in Barcelona's 4-1-2-3 formation, Messi never plays as a conventional striker. Instead the Argentine flows into spaces between the defensive lines, targeting gaps between the midfield and the back four, or sliding down the side of the left or right backs. The quality and unpredictability of his movement make him very difficult to mark.
Complicating the issue is the ability of David Villa and Pedro to play on the limits of the offside line. Both dart into offside positions then sprint back out, creating problems for defenders already conscious of Messi's transit.
Having faced Messi at Chelsea, Inter and Real Madrid, Mourinho's preferred method is to define a series of defensive zones and allocate Messi to a particular player according to the zone he travels into. Midfielders are stationed tight in front of the defensive line and tasked with harrying Messi and advised to tackle only when the chances of winning are high.
ŸOverall solution. The most telling defeat of Barcelona in a critical game was the first leg of last season's semi-final. Inter recovered a goal deficit to win 3-1, staying controlled in defence yet repeatedly opening up their opponents when attacking. The core of Mourinho's tactics was to close the space around Barca's forwards and midfielders while limiting what Mourinho calls "the depth" behind his own line.
He emphasised calmness, demonstrating to his players that a quick lateral pass away from the encircling Catalans would open the pitch up for a forward pass and counter-attack. Turned on their heels, or facing attackers running at them, Barcelona's defenders are relatively weak. The correct combination of clever organisation, patient concentration and focused aggression has undone them before. It could undo them again tomorrow.
Andrew Cole's memories of Barcelona, s8