Tammy Abraham completed the late turnaround for Chelsea at the Emirates Stadium as Frank Lampard's side edged past the Gunners in the Premier League.
A disaster start for Chelsea in the first-half was changed for jubilant and euphoric scenes at the Emirates in the final stages.
Pierre Aubameyang opened the scoring, but late goals from Jorginho and Tammy Abraham secured a vital win for the Blues.
Frank Lampard's side came out the blocks extremely slow. Mikel Arteta's men looked up for it, and they got their just reward 13 minutes into the London derby.
From a set-piece - a vulnerable area for the Blues this season - David Luiz flicked it on and it fell to Aubameyang who steered his effort past Kepa Arrizabalaga to give the hosts a deserved lead.
Emerson Palmieri was caught napping for the goal, and didn't enjoy his 30 minutes or so on the pitch. Frank Lampard was aware of his performance, and substituted him after the half hour mark for Jorginho as the Blues switched back to a four at the back system.
Chelsea looked much better in the second-half and grew into the game, but the derby didn't play out without controversy. Jorginho was initially booked for pulling back Alexandre Lacazette, and was then involved in another foul with Mateo Guendouzi. However, the referee didn't adjudge it to be a second bookable offence.
Frank Lampard rolled the dice and threw on Tariq Lamptey for his Chelsea debut, and also brought on Callum Hudson-Odoi; and the pair changed the game for the Blues. They added pace and intent and the Blues got their reward with eight minutes to go.
Mason Mount whipped in a free-kick, Leno missed the ball by punching the air and Jorginho was there at the back stick to tap it home to level the scores up in north London.
But Chelsea weren't finished there; Tammy Abraham had the last laugh as he fired it past Leno to secure all three points for Chelsea with a couple of minutes to go.
Chelsea broke through Tammy Abraham, he played Willian in; instead of finding an effort at goal, he took it to the byline to play it back to the forward, and Abraham neatly put it past the Arsenal keeper to send the away end into jubilation and euphoria.
Chelsea's defeat on Boxing Day is forgotten about for the time being. Back-to-back away wins against two London sides, both in north London, is no easy feat and Frank Lampard's side completed the job, just about.
They extend the gap in fourth to Tottenham and Arsenal, and now head to Brighton on New Years Day.
The Blues' away form has been much better than the form shown at Stamford Bridge this season - can they continue their momentum on the road again in a few days time on the south coast?