Derbies always have high intensity and the game is only more dramatic when the rivalry is as fierce as the one between Arsenal and Chelsea. Guus Hiddink's side, which has so often struggled to keep up with opponents this season, were industrious and resolute in their victory at the Emirates this weekend, leaving Arsenal players seething in what was undoubtedly one of the west London club's best performances of the season.
Make no mistake, Arsene Wenger's men are still very much title contenders, just three points off Leicester City, and Chelsea remain in the bottom half of the table, seven points from the relegation zone.
But the emboldening confidence that has boostered Chelsea after this game will carry them into next week, while the disheartening loss was only made more bearable for the north London side by the absence of Jose Mourinho in the away team's dugout.
Per Mertesacker's red card a crucial moment
The champions gained an early advantage with the dismissal of centre-back Per Mertesacker for a clip on Diego Costa. The Spanish international slipped past the defender, who in turn made a reckless tackle and earned himself a red card from referee Mark Clattenburg.
There was not much controversy over what seemed to be a rather cut and dry call, but home fans were less than enthused by Costa's histrionic reaction to the challenge. Nevertheless, from minute 18 onward, Chelsea had a one-man advantage which they wasted no time in exploiting.
Costa seals it for Chelsea
Like a vision from the past, Costa was unstoppable and intimidating in the attack on Sunday, notching his fifth goal in his last five games to win the game for the Blues. His goal, assisted by a well put cross from Branislav Ivanovic, came just five minutes after Mertesacker was sent off.
As the Gunner's defence watched the Spaniard nick the ball in past former Blue Petr Cech, it seemed not only as if Gabriel and Laurent Koscielny did not know how to react to Costa this time around, but also that Costa was ready to torment them for that.