If their men in the middle prove to be masters of their domain, Manchester United will falter.
In an irony probably not lost on either manager, Jose Mourinho and Arsene Wenger have more in common right now than they'd care to admit.
In midfield, there is an embarrassment of riches. Up front, there is the risk of being richly embarrassed.
The Gunners may not be overwhelmed by midfield quality, but they are spoilt for choice compared to their paltry offerings in attack. Chelsea know the feeling.
The two halves of Manchester have divided the best of the Premier League's goal-scoring machines among themselves, leaving both Mourinho and Wenger doing a headless chicken double act in the final days of the transfer market.
The performances against Hull City and Aston Villa underlined Chelsea's shortcomings to their manager. The keys to the EPL kingdom will not be entrusted to Fernando Torres, Demba Ba or Romelo Lukaku. Lukaku remains the best bet in the long-term, but he remains an apprentice.
The sorcerers are huddled together around the centre circle cauldron. Mourinho's magic must be conjured from midfield. Old Trafford is an intimidating fortress, but the hosts' midfield is by no means impregnable. Michael Carrick remains a resolute gatekeeper, but if he can be isolated, the Red Devils' drawbridge can be pulled down.
Just as Mourinho and Wenger obsess over new strikers, United manager David Moyes frets over his threadbare midfield. Many of his rumoured targets have been creative string-pullers; men who specialise between the lines.