It has taken several weeks, while his team have battled on to win games regardless, for Carlo Ancelotti to come to terms with identifying the positional requirement most effective for his expensive signing, Fernando Torres. So unsettling has the Spaniard's arrival appeared at Stamford Bridge that anoraks will recall the upheaval caused at Manchester City and, more recently, Newcastle with the signing of Rodney Marsh and Faustino Asprilla respectively. Torres may have to wait for his chance to make an impact from the bench on Sunday.

Yet Sir Alex Ferguson encountered a similar conundrum in assimilation when Javier Hernández, his Little Pea, blossomed to challenge the laconic craft of his Bulgarian goalscorer, Dimitar Berbatov. Just as Didier Drogba was central to everything at Chelsea, so Wayne Rooney was the main factor at United: to have a partner, or to stay single? Sir Alex's solution against Chelsea will see Hernández's sharp running and eagle-eyed movement looking to shift the visitors' captain, John Terry, while Rooney roams behind, linking the play and seeking space.

It is how Chelsea, and Mikel John Obi, react to that threat that could be key in this game. Mikel is vital as he plays with his head as well as his heart. He must not chase the ball. He must keep Rooney in sight. He must deter him by fair means in the tackle. He must not be drawn too wide and, most importantly of all, must not be drawn too deep. Discipline is so vital in this role. If the visitors are to become the first side to prevail at United this season, Mikel must play the Claude Makelele role better than the man himself.

In Chelsea's rejuvenated 4-3-3, the holding central midfielder has to be perfect in his decision-making so Frank Lampard can go forward and support with confidence, while also giving Michael Essien the security when he moves out wider to confront the advances of Patrice Evra. At Arsenal last week, Rooney, dropping off Hernández to help Michael Carrick and Anderson, never commanded enough ball to control the stage. Alex Song was key, snapping confidently in a more athletic Arsenal midfield, supplemented by Aaron Ramsey and Jack Wilshere.

Expect Carrick to hold his ground, but the evergreen Ryan Giggs will need to combine with Rooney to supply the United wide men against Branislav Ivanovic and Ashley Cole. The Chelsea full-backs themselves must be brave and advance whenever opportunities arise to maintain the width. But, once again, they will only feel comfortable doing that if Mikel is controlling his territory and offering assurance.

Furthermore, David Luiz, for all his brilliant individual technical skill and buccaneering surges, has a mistake in him, whether it be a wild tackle or a rush of blood provoking a forward run. He can be overconfident and overelaborate at times, susceptible to wild movements, so Mikel must be ever ready to step back and cover Terry when the Brazilian goes wandering. The central midfielder has never truly won the hearts of the Chelsea faithful, but on Sunday his contribution may just supply the title race with an incredible twist.