Arsene Wenger described his 1000th match in charge as one of his lowest days as Arsenal manager after his side were hammered by Chelsea.
The Frenchman, branded "a specialist in failure" by Jose Mourinho last month, remains without a win in 11 attempts against his nemesis after a spectacular implosion and a horrendous error by referee Andre Marriner, who mistakenly sent off Kieran Gibbs.
However, Wenger, who lost his 500th game 1-0 at Stamford Bridge said: "This defeat is my fault, I take full responsibility for it. I don't think there's too much need to talk about the mistakes we made. We got a good hiding. It's one of the worst days [of my career]. It was over after 20 minutes and it's a long game after that. You don't prepare all week to experience that."
Chelsea were already 2-0 up through Samuel Eto'o and Andre Schurrle before Gibbs was red-carded in the 15th minute. Eden Hazard's shot was handled in the area and despite Alex Oxlade- Chamberlain appearing to approach the official to admit his guilt, Marriner instead dismissed Gibbs.
Hazard converted the penalty to give Chelsea a 3-0 advantage. Oscar added a fourth before the interval and a fifth after 66 minutes before his replacement Mohamed Salah struck his first Chelsea goal as Mourinho's responded in style to the controversial loss at Aston Villa. In November, Marriner awarded Chelsea a controversial last-gasp penalty against West Brom at Stamford Bridge when it appeared Ramires had dived. Hazard scored on that occasion to earn a draw that preserved Mourinho's unbeaten Premier League record at home, which now stands at 76 matches.
It is likely Oxlade-Chamberlain, rather than Gibbs, will serve the suspension if Arsenal appeal or the Football Association intervene.
With eight games remaining, Chelsea top the standings having played more matches than their three rivals, but Wenger's title chance seems to have slipped and regaining the FA Cup won in 2005 appears to be Arsenal's only chance of ending their silverware search. In yesterday's opening exchanges Petr Cech was at full stretch to turn away an Olivier Giroud effort before a direct run from Schurrle led to the opening goal.
The German fed Eto'o, who turned Oxlade-Chamberlain outside and then in before curling left-footed across Wojciech Szczesny for his 11th goal of the season. Soon afterwards it was two after Nemanja Matic dispossessed Tomas Rosicky and found Schurrle, whose shot through three bodies found the net.
Worse was to follow when Hazard's shot beat Szczesny and Oxlade- Chamberlain dived to his left to handle the shot, which was going wide. Hazard scored from the spot and despite Arsenal sending on Thomas Vermaelen for Lukas Podolski, Oscar added a fourth for Chelsea after 42 minutes, tapping in from a cross by Fernando Torres, who had replaced the injured Eto'o.
Oxlade-Chamberlain and Laurent Koscielny were replaced at half-time as Wenger tried to stop the rot.
Arsenal's misery continued when the defence backed off and allowed Oscar to shoot from the edge of the area, with Szczesny less than convincing in being beaten for a fifth time. Salah completed the rout by shooting home under Szczesny after racing on to Matic's lofted pass.
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