The Germany international missed last weekend’s encounter with Stoke City due to a foot injury.
The Gunners suffered an early blow when Mertesacker was sent off for bringing down Diego Costa as the last man.
Arsenal conceded just minutes later when Costa made the most of some questionable defending.
Mesut Ozil’s 100th game for the north London based club ended in a disappointing defeat. Arsenal would have ended the week as league leaders had they beat the Blues.
The North London based side have now slipped down to third place and are just two points ahead of their bitter rivals Tottenham.
Following the game we took to social media to see how Ozil’s performance went down with fans. The 27-year-old received a mixed reaction from fans for his display yesterday afternoon.