When Chelsea visited the Emirates Stadium to face Arsenal earlier this season, it was Juan Mata who proved the difference. The diminutive Spaniard was inspirational, grabbing an assist for Fernando Torres' opening strike before finishing off a fine performance with the winning goal.
He has been one of Chelsea's best performers again this season, and when the Blues come face-to-face with the Gunners in the Premier League on Sunday, he will no doubt prove just as menacing.
With the arrival of Demba Ba this month, Chelsea have other threats in attack, but in Theo Walcott, Arsenal themselves have a man who is a potent threat going forward, as his recent goalscoring form has shown.
We take a look at where this mouthwatering London derby could be won and lost.