Arsene Wenger marked his 1000th match in charge of Arsenal with perhaps the most chaotic game of them all as his side were dismantled by Chelsea and were the victims of mistaken identity by referee Andre Marriner.
Goals from Samuel Eto'o and Andre Schurrle hurtled Chelsea into a 2-0 lead within the opening seven minutes as Arsenal's defence disintegrated before the match exploded with one of the most bizarre incidents seen in Wenger's 18 years at the helm.
An Eden Hazard shot was swerving wide but Alex Oxlade-Chamberlain threw his hand out and touched the ball as it fizzed past the post. Referee Marriner awarded a penalty and then astonishingly sent off Kieran Gibbs rather than Oxlade-Chamberlain, who even approached the referee to admit it was his misdemeanour. To make matters worse, the red card was incorrect as the handball had not denied a goalscoring opportunity, with the ball already going wide.
Hazard stepped up to take the penalty and made no mistake and Oscar added a fourth goal before half-time, capping a crazy 45 minutes. At half-time, Marriner admitted to BBC Radio 5 Live that he had made a mistake and the FA also sent out tweets detailing the appeals process for a case of mistaken identity.
Oscar crashed in a fifth goal - his second of the match - midway through the second half, although Wojciech Szczesny in the Arsenal goal was beaten by the bounce of the ball just in front of him, before Mohamed Salah scored his first goal for the club to make it 6-0. That equalled the record margin of defeat suffered by Arsenal under Wenger, alongside the 8-2 thrashing by Manchester United in August 2011.
The result leaves Arsenal seven points behind Premier League leaders Chelsea, although Wenger's side do have a game in hand.
Stamford Bridge revelled in the success, roaring "Arsene Wenger, we want you to stay" and "specialist in failure".
Marriner has previous at Stamford Bridge this season, awarding Chelsea a controversial last-gasp penalty against West Brom in November when it appeared Ramires dived. Hazard scored on that occasion to earn a draw in a result which preserved Mourinho's unbeaten Premier League record at home, which now stands at 76 matches.
The only saving grace on this occasion was that the decision did not appear to impact on the result and it is likely that Oxlade-Chamberlain will serve the suspension if Arsenal appeal or the FA 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 the Gunners' only opportunity of ending their silverware search.
Mourinho made his "failure" barb - referring to Wenger's eight-year trophy drought - after the Frenchman suggested anyone playing down their team's title chances was doing so for fear of falling short.
It ended the truce which had broken out in Mourinho's absence from the Premier League and, ahead of their third meeting of the season, Mourinho stopped short of joining those paying tribute to Wenger ahead of his landmark match.
Wenger's 500th game was a loss to Chelsea in August 2006 and there were warnings in the opening skirmishes of a repeat as Schurrle and Eto'o exposed gaping holes in the Gunners defence.
Petr Cech was at full stretch to turn away an Olivier Giroud effort before a direct run from Schurrle led to the opening goal. Schurrle 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, all of which have come at home.
Soon after it was two after Nemanja Matic dispossessed Tomas Rosicky and found Schurrle, whose shot through three bodies found the corner of the net.
After the 6-3 loss at the Etihad Stadium and 5-1 defeat at Anfield, the sinking feeling on a Saturday lunchtime was familiar for the Gunners. 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.
Marriner awarded a penalty and thought the offender was Gibbs, seemingly refusing to be persuaded otherwise by Oxlade-Chamberlain, and Hazard converted the spot-kick after the mayhem had subsided.
Thomas Vermaelen went on for Lukas Podolski, but the Gunners leaked a fourth three minutes before half-time when Fernando Torres, on for the injured Eto'o, crossed for Oscar to tap in.
Oxlade-Chamberlain and Laurent Koscielny did not reappear for the second half as Wenger made two further substitutions in an effort to stop the rot.
Torres had a mazy run halted by Per Mertesacker and the ball broke for David Luiz, whose shot was saved by Szczesny, while there was a rare Arsenal attack which saw Santi Cazorla flash a shot across goal after 60 minutes.
Arsenal's miserable afternoon 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 replaced Oscar and soon after netted under Szczesny after racing on to Matic's lofted pass, completing the rout.