So far it's been an attacking, free-flowing World Cup full of goals, fun and surprises. Now, enter Iran.Every tournament should have one: the mysterious team from a political-pariah nation who play dourly and defensively. At least, that's how we think they'll play. Iran's players mostly do their business in the country's own domestic league, which tends not to turn up on Sky Sports very often. So they're the biggest unknown quantity in the tournament.Iran topped a qualifying group that included Lebanon, Qatar and Uzbekistan, scoring eight goals and conceding two in eight matches. Among the low-scoring games were two grinding 1-0 wins against South Korea and, with former Portugal boss and Man United deputy Carlos Quieroz in charge, their defenders will be drilled with fanatical precision.There's some flair up top, though: Fulham fans know Ashkan Dejagah has got the moves when he can summon up the energy, while striker Reza Ghoochannejhad arrives after another blistering season for Charlton Athletic: one goal in 17 appearances. The secret weapon might be veteran midfielder Javad Nekounam, who at 33 years old is a more prolific goalscorer than any of the team's strikers.Iran can't afford to start too cautiously in their first game, since it's by far their best chance of picking up a win. Their opponents today should be too good for them, but it's not a given: although Nigeria won last year's African Nations Cup, they lack the sort of freewheeling creativity that might unlock Iran. Instead they rely on pace and power, and normally prefer to counter-attack in a way that won't be an option in this game.Nigeria also have the perennial problem faced by so-so international sides: their best players don't fit together very well. Jon Obi Mikel plays a lot further forward than he does for Chelsea, with Victor Moses and particularly Peter Odemwingie also not enjoying a settled position. That said, Emmanuel Emenike is a solid finisher, and look out for the ludicrously quick Ahmed Musa on the right side of their attack.