Never mind Arsenal just fans...the sight of Cesc Fabregas in a Chelsea shirt and in a Jose Mourinho team is a strange one for football followers in general.
While that reality is taking time to sink in, Mourinho has been getting the best out of a player carefully nurtured by Arsene Wenger.
In many ways, Fabregas represents the difference between the two managers over the years. Wenger builds the mansion, Mourinho moves in with the pet rottweiler when the walls have been painted and the furniture has already been put in place.
Wenger isn't normally for turning but surely even he can see that he will need to adapt his tactics against Mourinho who has always tended to have the upper hand on him.
The Gunners go into Sunday's match at Chelsea with some degree of confidence after the midweek win over Galatasaray.
But the Blues are a far different proposition...
The Dangers
Chelsea will not look to press the Arsenal centre-backs. Instead the template that worked last season during the 6 - 0 win at Stamford Bridge was to harry the midfielders and dart into the space that the Gunners normally leave behind the full-backs and in the zone where the defensive midfielder can be overwhelmed by pace and movement.
Diego Costa is another added weapon on Sunday with the Spain internationals tendency to work the channels between centre-backs and full-backs.
Do not be surprised if he targets the positionally strong but oil tanker slow Per Mertesacker on the break rather than Laurent Koscielny.
With the height and power often exuded by Mourinho teams, Arsenal will also have to be extra careful at set pieces.
Solutions?
Arsenal now have pace to burn which means they can be far more vertical (move from back to front more quickly) in this game. Alexis Sanchez and Alex Oxlade-Chamberlain are both solid with tracking back and have the speed to move in transition in attacking sense which would help quell one of Chelsea's strengths.
Playing Mesut Ozil behind Danny Welbeck will also allow the German to have a greater influence on proceedings and also allow him to utilize his immense ability to thread through balls.
The midfield pair of Mathieu Flamini - and one other - would be advised to sit deeper than normal both to squeeze the space between defence and midfield and also to make play more vertical, while Stewart Robson's suggestion to play a quasi-three at the back (Calum Chambers tucking in from right back) when attacking would be a smart move in terms of protecting the channels and having more bodies behind the play.
But the most crucial thing is to keep things tight early on as Chelsea are not the type of team to give up a lead very easily and indeed can punish teams searching for an equaliser.
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