Chelsea ruined Arsenal manager Mikel Arteta's home debut as Tammy Abraham's late strike sealed a dramatic 2-1 win after Bernd Leno's horrific blunder turned the tide in a thrilling London derby on Sunday.
Leading through Pierre-Emerick Aubameyang's early goal at the Emirates Stadium, Arteta was just seven minutes away from securing his first victory in his second game in charge.
But Gunners goalkeeper Leno made a hash of coming to catch a free-kick and Jorginho tapped in to spark a Chelsea fightback that climaxed in Abraham firing home with three minutes left.
After dominating the first half, it was a shocking but familiar collapse from Arsenal, whose lack of steel was the key element in the downfall of Arteta's predecessor Unai Emery.
In their final game of the decade, Arsenal showed just how much work Arteta has to do to steer the Gunners back to respectability in his first managerial role.
After coming from behind to rescue a 1-1 draw at Bournemouth in his first match on Thursday, Arteta would have been encouraged by their bright start -- but not the woeful meltdown that leaves Arsenal with only one win in their last 15 games in all competitions.
Arsenal, 12 points adrift of the top four, have lost four consecutive home fixtures in all competitions for the first time in 60 years.
They also suffered three successive top-flight home defeats for the first time since 1977.
While Arteta held his head in despair after Abraham's winner, Frank Lampard's wild celebration showed Chelsea's need for the win after a difficult period of their own.
Fourth placed Chelsea had lost five of their last seven league games, but a second successive away win -- following their recent impressive success at Tottenham -- moves them four points clear of fifth placed Manchester United.
There was no fanfare for Arteta before kick-off, the Spaniard quietly take his place on the bench to applause from Arsenal fans but without any elaborate introduction.
Chelsea went close early on when Willian's quick free-kick caught Arsenal flat-footed, allowing Mason Mount to drift into space for a fierce strike that stung Leno's palms.
But, initially vibrant in possession and tireless without the ball, Arsenal exposed Chelsea's own problems at the back to take the lead with a well-rehearsed set-piece routine in the 13th minute.
Calum Chambers was positioned perfectly to rise above Fikayo Tomori and glance Mesut Ozil's corner towards Aubameyang.
The Gabon striker, who also scored in Arteta's first game, applied the finishing touch, escaping Emerson's slack marking to guide a diving header past Kepa Arrizabalaga for his 15th goal of the season.
Arteta didn't hide his delight, fist-pumping in celebration of the first home goal of his reign.
Aubameyang's goal meant Chelsea had kept just two clean sheets in their last 11 league fixtures and, with Arsenal well on top and threatening to score again, Lampard was forced to take drastic action.
In a bid to shake Chelsea out of their lethargy, Lampard hauled off Brazilian wing-back Emerson and sent on Italy midfielder Jorginho as he ditched his 3-4-3 formation after just 33 minutes.
The switch proved an inspired move but not before Mount, N'Golo Kante and Antonio Rudiger were all booked in quick succession as Chelsea used brute blunt Arsenal's momentum.
Chelsea were on top in the second half and teenage debutant Tariq Lamptey led the charge when his surge ended with Abraham's shot being blocked by David Luiz.
Leno's game-changing 83rd minute howler was truly farcical, the German lying with his head in his hands after his misjudgement of Mount's high free-kick allowed Jorginho to tap into the empty net.
Suddenly, Arsenal reverted to their nervous former selves and Chelsea took full advantage to complete a remarkable fightback four minutes later.
Willian broke into the Arsenal area and crossed to Abraham, who turned unchecked by the ponderous Shkodran Mustafi to fire a cool strike under Leno.