They are on the verge of an extraordinary quadruple. Andres Iniesta and Xavi Hernandez have already won the European Championship with Spain and the domestic league and cup double with Barcelona. Tonight they could make it four major honours in 12 months. Here is The Independent's guide to the midfield marvels and how they pull Barça's strings.
1. The passes
As Sir Alex Ferguson famously said recently: "I don't think Iniesta and Xavi have ever given the ball away in their lives." When Xavi was voted the best player of the last European Championship it was on the basis of some amazing passing statistics. The midfielder played 254 passes throughout the tournament at an 89 per cent success rate.
There was a time when his allergy to giving the ball away counted against him. Xavi was criticised when the club went two years without winning a trophy for veering on the side of caution and playing too many safe passes. He admits to benefiting from the injection of urgency and the insistence on end product that Guardiola has brought to the side. He says: "The rhythm and the speed of our play has changed. Everything is one-touch now with no unnecessary elaboration."
Barça will look to play their usual keep-ball tonight aided by a willingness to get as many bodies into the middle of the pitch as possible. One central defender usually goes out wide to receive keeper Victor Valdes' throw and the full-back on that side pushes up, making a fourth midfielder.
2. The goals
Leo Messi, Samuel Eto'o and Thierry Henry might be the world's most prolific forward line with 97 goals in all competitions this season, but in 360 minutes of football against Premier League sides over the last two seasons they have failed to score. Messi has in fact never scored against an English side. Should the hoodoo continue tonight Barça will once again be relying on Iniesta and Xavi. They are used to loading the bullets from midfield but as Iniesta showed at Stamford Bridge – when needs must they are also capable of pulling the trigger. "I was very close to him and I thought he would control it and give it to me. It was a good thing he didn't pay me any attention" says Xavi of the goal against Chelsea.
Iniesta says: "There was no time to think, I just hit it." Both players prefer to play a pass even when receiving the ball on the edge of the box but if United plug all the gaps as Chelsea did, then expect them to go for goal.
3. The inheritance
Both players came through Barcelona's famous school of Excellence "La Masia" where they had pictures of their now coach Pep Guardiola on their bedroom walls. At the time Guardiola was pulling the strings and wearing the captain's arm-band in Barça's so-called "Dream Team" midfield but right from the start it was clear that he would pass the baton on to his two protégés. In an interview eight years ago the still-playing Guardiola said of Xavi: "It is fundamental that Barcelona do not let him leave. In the next 10 years, whoever the coach is, he is going to be vital to this team. He has something that other players do not have – it is the way he sees the game. I will be watching him from the stands." Iniesta says of his hero turned boss: "He represents so much to me. He was my idol and now he is coaching me. It is incredible."
4. The telepathy
"All we do on the pitch is put into practice what we learnt in La Masia," says Xavi. He started training with Barcelona aged 10. Iniesta was spotted aged 12 and both will have been playing one-touch pass and move football in a 4-3-3 formation since they were old enough to play 11-a-side. "He is the best team-mate I can have and the best footballer Spain has by a long distance because he can do things that other players can't do" says Xavi. Iniesta says: "Something is missing from the team when Xavi is not playing." As well as sharing a football education at La Masia the pair also share the disappointment of missing out on Barça's last Champions League win against Arsenal. Xavi was still recuperating from injury and Iniesta was surprisingly left out of the starting XI. Iniesta remembers: "Everyone was saying that I was going to play but I could sense that maybe I would not start the game."
Xavi recalls: "I don't know if it was Henk Ten Cate's decision or Frank Rijkaard's but at least he came on to turn the game around in the second half." Iniesta came on with Barcelona 1-0 down at half-time and was instrumental in the turnaround that saw them win 2-1. The importance of the double act to Barcelona this season was underlined by the only dip the team suffered coinciding with Iniesta's longest injury. He strained a thigh on 17 February and before he could return on 3 March, Barça had been beaten by Atletico Madrid and Espanyol and drawn 1-1 in Lyons in the Champions League.
5. The fame
Things could change if they get the better of Anderson, Giggs and Carrick tonight... but it is unlikely. "I couldn't care less about the marketing side of things" says Iniesta. "I have the respect of so many people and that matters more to me." There is no Ronaldo suntan for the man whose skin is so white he glows in the dark when depicted on a famous Catalan TV show that sends up the entire squad. The only real concession to fame is his Granddad's bar – now an Iniesta museum that houses a small Barcelona supporters' group and just about every newspaper cutting that ever mentioned his name pasted on to the walls. Xavi meanwhile appears with other members of the Spain team in a beer commercial. Neither man was made for the catwalk although as Sir Alex Ferguson says: "They get you on that carousel and they can leave you dizzy."
Homage to Catalonia: In praise of Barça aces
"Xavi is particularly special – the evidence was there at the European Championship." David Villa
"Xavi epitomises the Spanish style. He is extremely influential in the whole possession, passing and penetrating kind of game Spain play." Andy Roxburgh
"This kid will retire me." Pep Guardiola
"The way he finds passes; his movement and ability to create space is incredible." Sir Alex Ferguson
"The best player I have ever seen." Pep Guardiola
"He is the complete footballer. He can attack and defend, create and score." Vincent Del Bosque
"He's always been good: it surprises me that it's taken so long for people to discover him." Victor Valdes
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