Arsenal played much of the contest with 10 men after Kieran Gibbs was sent off a quarter of an hour into the match due to an error by the referee, who mistakenly cited the left back for a hand ball in the penalty area even though the real culprit was his teammate, Alex Oxlade-Chamberlain.
Arsenal was already down 2-0 at the time and the margin was increased to three shortly thereafter when Eden Hazard converted the penalty kick.
Samuel Eto’o opened the scoring in the fifth minute off a pass from Andre Schurrle and the German got a goal of his own two minutes later when he capitalised on an error by Arsenal defender Santi Cazorla and fired a shot past Polish goalkeeper Wojciech Szczesny.
Jose Mourinho’s squad piled it on after Gibbs’ expulsion, with Brazil’s Oscar scoring goals in the 42nd and 66th minutes and Egypt’s Mohamed Salah adding insult to injury in the 71st minute.
With the lopsided victory, first-place Chelsea extended its lead in the Premier League to seven points over Liverpool and Arsenal.
The Gunners, who have played one fewer game than Chelsea, came into the London derby without some of their key players, including Jack Wilshere, Aaron Ramsey, Theo Walcott and Mesut Özil.
The 64-year-old Wenger acknowledged afterward that the match was one of his worst days at the helm of Arsenal, a team he has guided to three Premier League titles and four FA Cup crowns.