Wayne Rooney v Carlos TevezFor the first time, the question can be asked: have United become a one-man team? Until now, United could always attack from so many different areas of the pitch, but their progress this season is about the impact of one man - Wayne Rooney.
The England striker is thriving on the responsibility of being the big noise in the orchestra.
Here, he could be the difference between them going through and going out.
Key battle: Wayne Rooney and Carlos Tevez battle for the ball in last week's first leg of the Carling Cup semi-final
The same can be said of Carlos Tevez, in the opposite corner in what feels like an old Western shoot-out between two in-form strikers and former team-mates.
Both are scoring goals and carrying their teams. You could see that Tevez was not match fit earlier in the season when he was playing with injuries, but he is on his top game now.
He will lead the line for City and may have to cope without much support in stages this evening, but that will not impact on his ability to run and chase lost causes. He will be a menace to the United defenders.
Rooney is playing with control of his emotions and Tevez will require that too, although he has played in some of the world's biggest derbies.
The threat of Craig BellamyGetting shirty: United will need to keep a close eye on Craig Bellamy at Old Trafford
Tevez is City's form player, but their best operator this season has been Craig Bellamy. Electric pace, consistency and danger - and it seems he's seen off Robinho.
Players remember grounds where they have put in a specialperformance and Bellamy will return to Old Trafford confident after hisdestruction of Rio Ferdinand in the Premier League game this season,won 4-3 by United.
That day, United could not live with Bellamy and he gave the youngright back, Rafael, another chasing in the first leg of this CarlingCup semi-final.
He will be crucial to City's counter-attacking style, when they arelikely to sit deep with five in midfield, including Bellamy, and thenlook to break.
The Welshman will be key to supporting Tevez andto isolate United's full-back. Rafael is likely to play and will needsupport, in the absence of the dogged John O'Shea. Imagine if Sir AlexFerguson picked Gary Neville instead now that would be interestingto see him on the same pitch as Tevez!
City cannot try to play too defensively, because that will just invite United on to them. They have to get out and attack too.
Antonio Valencia v Javier GarridoUnited will attempt to get at City along their left wing. With Bellamy ahead of Javier Garrido, United will expect to create chances from this area.
Antonio Valencia has done well for them. He has stepped into big shoes by replacing Cristiano Ronaldo, but he has made an impact at Old Trafford and I expect him to see plenty of the ball in the opening exchanges.
He was dangerous in the first half at City and United's goal came from his right-wing cross, when Bellamy was unsuccessful in closing him down.
Making his mark: But will Manchester United winger Antonio Valencia make it a miserable night for Javier Garrido at Old Trafford?
United will look to isolate Garrido, who has a sweet left foot but is vulnerable defensively. It could be a key area of the match.
Valencia is quick, direct and growing in confidence. On some occasions, his crossing has been spectacular, although he can also disappoint with his final ball.
It's a game that requires the best players to be at their best. I will be there for Sky and cannot wait.
It's a match with a sense of devilment and drama about it; a game where we will all be perched on the edge of our seats. I'm backing United to win 3-1. But it will be tight.
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