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I don't think people will be worried if Chelsea loses to Arsenal, but what is worried is if Chelsea can beat Arsenal. So far, Chelsea has also performed poorly in home matches, winning only 1 of 4 matches. Chelsea have suffered two defeats at home, but I think they will avoid a third defeat this week for the derby. Arsenal is the favorite, but Chelsea cannot be said to be bad.
Derby always tends to be interesting and the form Chelsea are in right now, a win against Arsenal in London derby will give a big statement to Chelsea fans. Arsenal are certainly favourites but Chelsea shouldn't be underestimated with the squad they have. All it takes is one goal and defend till the end to win the game and if they have a perfect gameplan against Arsenal and execute it well then they also have a chance. However I am rooting in for Arsenal as they have got the lead against City and now we have to perform consistently and we have to win these kind of matches also which are a big hurdle for us in the title race.