Barcelona must beware the artful dodgers of the Champions League in Saturday's final at Wembley where Manchester United will get a second chance to pick the pocket of Europe's classiest team.

United, who have snatched two Champions League final wins from what appeared to be certain defeats, were overwhelmed by Barca's precision passing game when the teams met in Rome in 2009, surrendering in a one-sided 2-0 defeat.

Two years on, the only certainty on the vast Wembley pitch is that the Spanish champions, boasting the world's best player in Lionel Messi, will again enjoy the bulk of possession.

But while Barcelona remain technically superior, no one could ever accuse wily United manager Alex Ferguson of failing to learn from his mistakes.

With England striker Wayne Rooney and the exciting Mexico forward Javier Hernandez among the talent at his disposal, an upset is far from beyond their grasp.

"We are not scared of Barcelona," South Korean midfielder Park Ji-sung, part of the team that lost to Barcelona two years ago, told reporters this week.

"They are one of the best teams in the world, but we have our own quality," he added.

United clearly do have quality but it will need temperament as well as talent to prevail in a battle between two clubs who each have three European Cup wins, and curiously enough won the first of them at the old Wembley Stadium.

Guardiola was part of the Barca side that triumphed at last in 1992, with a 1-0 victory over Sampdoria under the venue's famous Twin Towers.

It was back in 1968 when United won their first European Cup with a 4-1 Wembley victory, also in extra time, against Benfica.

The two subsequent wins for the English side have been a case of victories conjured from seemingly hopeless situations.

The first came at Barcelona's Nou Camp stadium in 1999, when two last-gasp goals earned them a sensational 2-1 win over Bayern Munich in a match that had appeared lost.

In 2008, they were staring at defeat again when Chelsea captain John Terry had a chance to win the title in a penalty shootout in Moscow only to slip, miss and gift United the opportunity to win their third European Cup.

There was no such escape against Barca in Rome the following year, as Guardiola capped a perfect first season in charge by masterminding a comprehensive win over United that completed a treble of league, cup and Champions League.

If Barcelona are to be denied a third European title in six seasons -- they also beat Arsenal in 2006 under Frank Rijkaard -- United will have to be ruthless when chances come their way.

The quality of midfielders Xavi and Andres Iniesta, the beating heart of the Spain team that won the World Cup in South Africa, ensures Barca rarely cede control.

With Messi marauding through the middle it is inconceivable that United's defenders will have a carefree night.

The English side will rely on a rearguard built around the formidable central defensive pairing of Nemanja Vidic and Rio Ferdinand, while 39-year-old Edwin van der Sar, who will retire after the match, will need to bow out on a high.

The Dutch keeper will certainly have work to do against a side that look irresistible in attack and reached the final via the toughest of routes, beating arch-rivals Real Madrid over two bruising semi-final legs while United strolled past Schalke 04.

Messi has scored 52 goals this season in all competitions and is top scorer in the Champions League with 11 in 12 games.

The Argentine maestro will play as part of a three-man attack alongside Pedro and David Villa, both members of the Spain team that enjoyed World Cup glory last year.

United's hopes of avenging the 2009 defeat will rest on their ability to pick holes in a Barcelona defence that does occasionally have a threadbare look about it.

Rooney has played himself into form following a very public wobble in his enthusiasm for playing for Manchester United and Hernandez, nicknamed 'Chicharito', or 'Little Pea', has enjoyed a superb first season at the Old Trafford club.

With Welsh midfielder Ryan Giggs playing as well as ever, despite the tide of newspaper stories about his private life, United will rightly feel from overwhelmed going into Saturday's rematch, where they enjoy home country advantage.

The winners will lift their fourth European Cup in total and join Real Madrid and AC Milan as three-times winners in the Champions League era starting in 1992-93.

A United victory would take Ferguson level with Bob Paisley of Liverpool as the only manager to win the competition three times.

For Guardiola, it would be a second Champions League title in just three seasons as a coach while confirming Barcelona as one of the great sides of this or any era.