5 Key factors in United-Arsenal showdownArsenal's PassingIt's a brand of football like we've never seen before; they flood forward in numbers and you are never quite sure where they are coming from or what they are going to do next.
They change the point of attack quickly, whether through Alexander Hleb, or Tomas Rosicky, or the remarkable Cesc Fabregas.
They are not the quickest team, but their speed comes from moving the ball at pace. It's like watching an ice hockey puck, the way it shifts across the surface.
The passing is crisp and faultless, one touch and deadly.
Everyone is talking about Arsenal and their football. Hands up if you wrote them off...
Arsenal's weakness at set-piecesUnited will look to take advantage of the home side's lack of height at the back; I noticed that Arsenal were fortunate at Liverpool to get away with it.
Good delivery from dangerous areas will invite Nemanja Vidic and Rio Ferdinand to attack the ball and it is an area where United will look to score.
Emmanuel AdebayorWhat a player. He looked tired against Liverpool last week and playing alone up front can have such an effect.
But his physical power and presence has allowed Arsenal to play a different way and to carry more threat from crosses.
You can also play the ball up to him and it will stick. He's scoring goals and looking dangerous.
United's rapid counter-attackWhat formation do United playÂ…does anyone know?
It's four at the back, then possibly two holding midfielders with the front four going wherever they wish, to cause maximum mayhem.
They will know that Arsenal attack in numbers, but they will wait for the break down.
Then advance at pace, with exceptional movement and variety and hit back on the counter attack.
Fergie will tell them: "Win back the ball and then just go and play."
Hargreaves vs FabregasThe key match-up. Owen Hargreaves was brought in to be a destroyer and now he has to do that against the fabulous Cesc Fabregas.
The England midfielder has made a stuttering start because of injury, but he has to find a way to put out the Fabregas fire.
When Arsenal have the ball, they are relentless. With Michael Carrick fit, maybe Hargreaves will get some help and United will go belt and braces with two holding midfielders.
It is where the game can be won.