By Phil McNulty
Chief football writer
Manchester United and Chelsea face each other in the most anticipated match of the Premiership season to date at Old Trafford on Sunday.
Sir Alex Ferguson's side will be looking to maintain a momentum that has put them on the Premiership summit and hinted at the first serious title chase between the pair since Jose Mourinho's arrival at Chelsea.
Former Chelsea and Scotland star Pat Nevin analyses the strengths of the two giants for BBC Sport and investigates the key areas where a crucial three points could be won or lost at Old Trafford.
Chelsea must choose between Carlo Cudicini and Hilario, and there is not that much difference. I would probably go with Cudicini for his experience of these types of games.
Do Man Utd have the edge in the goalkeeping department?
He may have weaknesses, but we are comparing him with Petr Cech, who is arguably the best in the world.
In the absence of Cech, you have to say United have the edge in the goalkeeping department.
Edwin van der Sar brings vast experience and has been an excellent signing.
It took United a long time to get Peter Schmeichel's successor sorted out, with Mark Bosnich, Massimo Taibi, Roy Carroll and Tim Howard all getting a chance prior to Van der Sar's arrival.
A club of Manchester United's size and stature deserves a world-class keeper and Van der Sar is in that category.
Some interesting selection decisions here. I think Chelsea will go for Khalid Boulahrouz at right-back because of his power, and despite criticism from some quarters, Ashley Cole will always get the vote as first choice ahead of Wayne Bridge on the other flank.
If you don't play an expansive game in terms of having wingers on the pitch, you need width from elsewhere, and there is no defender better than Cole at getting up and down the line.
Is Argentine Gabriel Heinze the best left-back in Britain?
Cole is not easy to pass, and he has relished clashes with Cristiano Ronaldo before at club and international level.
Patrice Evra has done well for United, but I regard Gabriel Heinze as the best left-back in Britain - and I think he is even better as a left-sided central defender. He would be my man for a game like this.
Defensively, I think United have the slight edge purely because of Van der Sar.
I think Chelsea are better through the middle with John Terry and Ricardo Carvalho, but United are better in the full-back department with Heinze and Gary Neville.
I think Neville has been outstanding this season. Much was made of his playing relationship with David Beckham, but I think he's better without him.
He gets beyond the midfield on more occasions and gets into better attacking positions, with Ronaldo inclined to move into the middle while Beckham remained static. Neville is playing a bolder game than we have seen from him and he has excelled.
Fascinating. You have United's classic midfield four, with two wide men, up against Chelsea's diamond formation without a traditional wide man.
Chelsea used a 4-3-3 or 4-5-1 last season, but the arrival of Andriy Shevchenko means they have switched to a 4-4-2.
I think if you cut Jose Mourinho open, it would reveal that in his heart he likes to play with wingers, but he is a pragmatist and will not play square pegs in round holes.
Makelele will attempt to break up Man Utd's forward momentum
Claude Makelele will lie the deepest of the four, playing a role that is not about tackling and negativity, but about intelligence and reading the game.
I can see him killing the space in front of the back four that Wayne Rooney is so brilliant at exploiting.
Neil Lennon did it in Celtic's Champions League win against United, and an added difference is that Makelele is the best in the world at it.
Louis Saha plays up front with Rooney just off, but I can see Makelele sitting in there to nullify this.
Chelsea will have Michael Essien on the left and Frank Lampard on the right of the diamond, with Michael Ballack at the point in the most attacking formation.
In truth those three are interchangeable, but I would have Ballack pushed forward.
United's midfield is more traditional, and it will be interesting to see if either manager blinks and changes formation. I would be surprised if they did.
I really admire United's attacking approach. Ryan Giggs, Ronaldo and Paul Scholes are all forward-thinking midfield players.
Michael Carrick has had criticism this season, but with that positive attitude, he is occasionally being asked to be the midfield. You can be out-numbered and it can lead to this sort of unfair criticism.
Usually United are in control of a game so it's not a problem. It is more of a problem when they come up against the best in the business and you are not controlling the game - so Sunday will be very interesting.
People argue that Wayne Rooney is world-class. There is no argument that Andriy Shevchenko is world-class.
Throw in that Didier Drogba is playing as well as any striker on the planet at the moment, and you have quite a formidable strike force.
Could Shevchenko, Rooney or Drogba grab the all-important goal?
Shevchenko has not flown off the blocks as he adapts to the Premiership, but do not question him. He is world class.
I spoke to Drogba recently and put the point to him about whether he has benefited from Shevchenko's arrival.
He told me he is more mature now, and also that there was never any question of him leaving to accommodate Shevchenko.
Mourinho told him as soon as it became clear Shevchenko was coming that he would be playing alongside him, not being replaced by him. Bold words from Mourinho, but a decision that is proving fruitful.
He realised they would have adapt to each other, and that is what they are doing.
The credit, however, must be given to Drogba's development as opposed to Shevchenko's arrival.
Comparisons were made between Drogba and Saha some time ago, but now you would have to say Drogba is some way ahead.
This is not to say Saha is a bad player, it is simply a sign of how well Chelsea's striker is playing.
Rooney will be key, but watch out for Makelele.
The difference that decides the game may not be in keepers, defence, midfield or strikers - it could be on the bench.
Chelsea have options and a strength in depth United cannot match.
Ferguson can shuffle his pack, whereas Mourinho can make decisive changes with players like Joe Cole, Arjen Robben, Shaun Wright-Phillips, Salomon Kalou and Jon Obi Mikel at his disposal.
This is where United were caught short against Celtic. They needed a goal, but were only able to put Patrice Evra and John O'Shea on.
It is a game that is too close to call - not a decisive game in terms of the Premiership but the most important so far.
United must keep on Chelsea's coat-tails until January, when they can strengthen. If they don't get re-inforcements then, Chelsea will win the title again without any doubt.
A draw would leave United still up there, but I don't think Chelsea would even see a defeat as desperate because I believe the strength of their squad gives them a feeling that United will weaken before they do.