Sir Alex Ferguson has three senior central strikers at his disposal: Dimitar Berbatov, Wayne Rooney and Carlos Tevez. They respectively cost (or will do if United take up their option on the latter) £31m, £28m and £20m. So who does he pick to lead the line in the most important match of the season so far? A winger.
In the early years the Manchester United manager made some tactical errors in European competition. He omitted Peter Schmeichel in Barcelona during the three-foreigner rule (Gary Walsh conceded four); he played David May at right-back in Gothenburg (he was withdrawn at half-time, destroyed by Jesper Blomqvist) and there were those gung-ho opening gambits at Old Trafford (which led to conceding early away goals against Borussia Dortmund and Monaco). However, Ferguson is a keen learner and in recent years he has got his European tactics right. Last night was no exception.
Ferguson picked Ronaldo at centre-forward in part because the Portuguese is no ordinary winger. He is brave (forget the rolling about, he always comes back for more, and remember the headed goal in Rome last season?), an excellent finisher and, despite the snake-hips, built like a Salford outhouse. He is six foot of muscle. Graeme Murty, the Reading captain and Scotland international full-back, once described in awe experiencing Ronaldo's power at close quarters.
So he can handle the physical aspect of playing at centre-forward, and meet the technical requirements of a goalscorer. However, the main reasons Ferguson frequently fields Ronaldo at centre-forward away from home in Europe are his pace, movement and two-footed play. The latter makes him a menace as defenders do not know which way to show him. His speed is a problem for most defenders. Off the ball he is happy to lead the line or drop off into areas where defenders are loath to follow. On it he drags them wide, to places where he is at home but centre-halves feel exposed.
There is one other bonus in giving him the No 9 role. Ronaldo cannot be trusted to track back. He is not as lazy as Ronaldinho, who refuses to do it, but he tends to stop when play breaks down, especially if he has been tackled, and is slow to get back into position. Ferguson, the arch-pragmatist, would not accept this from many players, but Ronaldo is special. Playing him in the centre, and those assiduous workhorses Wayne Rooney and Ji-sung Park on the flanks, means his defensive weakness is not an issue.
The opening goal was a classic example of his threat. Ferguson always asks his wingers to hug the flanks. This stretches a back four, creating spaces between the full-backs and central defenders. Ronaldo, having dropped off the back four, drove into one of those spaces (in what was once described as the inside-left channel) in pursuit of a beautifully-weighted ball from Anderson. Johan Djourou, who was too far from Ronaldo to start with, was unable to reach him before he played the first-time cross which turned the unfortunate Kieran Gibbs and resulted in Park's neat finish.
Later in the half came a less spectacular, but equalling telling example of his centre-forward play. Pulling off the back four he received possession from the midfield, then held on to it while the bear-like Alex Song clambered all over him. He went to the touchline, then twisted back inside leaving Song and Bacary Sagna flat-footed, before releasing a 20-yard shot. There were many other examples. It was a masterclass. He even held the ball better than Emmanuel Adebayor, Arsenal's 6ft4in traditionally built centre-forward.