Arsene Wenger only has himself to blame for his team's defensive blunders against Chelsea. Wenger has singled out the defensive gaffes that contributed to Chelsea's two goals as the reason for defeat, according to Sky Sports.
However, Wenger is the one who is culpable after inexplicably dropping Per Mertesacker in favour of Laurent Koscielny. The French stopper endured a calamitous performance and made a back four that has been stout and resilient this season look constantly fragile.
Koscielny doesn't deserve to be condemned for his own goal. He had to react to a dangerously and cleverly flighted free kick. Credit should got to Juan Mata for his teasing delivery.
However, it was Koscielny's wild display in open play that was truly horrifying to watch. It was easy to lose count of the number of times the ex-Lorient ace needlessly dived in and missed the ball, taking himself out of position and increasing the threat to Arsenal's goal.
In truth, it is Koscielny's style to step out of defense and rob or intercept possession through his athleticism and anticipation. Yet that mode of defending is exactly why Koscielny shouldn't have been picked.
First in terms of style, he is too similar to Thomas Vermaelen, who also takes chances to win the ball. Sound defensive partnerships are built on a complement of styles.
As a stay-at-home defender, Mertesacker provides that complement. Knowing the cerebral Germany international is going to maintain his position allows Vermaelen the freedom to attack forward players in his usual buccaneering manner.
Why then would Wenger make the change and opt for Koscielny? Considering Chelsea's attack, it's easy to see one line of reasoning that appears sound.
Chelsea are transforming their attack this season, relying on a forward line filled with quick and tricky ball players. Agility and speed are certainly not Mertesacker's best assets, and perhaps Koscielny's quickness was thought to be the best way to subdue Fernando Torres, Eden Hazard and Oscar.
Wenger suggested that the style of the opponents influenced his decision, according to Arsenal.com. However, this only appears like smart thinking.
Players like Hazard and Oscar rely on defenders taking gambles in the challenge. Their ability to niftily turn away from trouble or utilize a clever touch frequently outwits aggressive defending.
Anticipation and making clean tackles are probably Mertesacker's finest qualities. He's also intelligent enough to keep shifty players in front of him as much as possible.
The other element that contributes to a solid defensive pairing is continuity. Mertesacker and Vermaelen played in every Arsenal game up to the clash with Manchester City.
Koscielny had to step in against the Citizens, but by dropping Mertesacker for the Chelsea game, Wenger disrupted a back four that have grown used to one another. The defense already had to deal with goalkeeping issues, and a needless change in the middle only caused more problems.
The Vermaelen-Koscielny partnership is a poor one, and Mertesacker had done nothing to merit the decision not to include him against the league leaders. The defensive formula was working, so why change it? That's the question Wenger should answer.