Chelsea came into their Premier League clash with Arsenal as massive favourites on Wednesday night.
Having reached both the Champions League and FA Cup finals, the Blues entered the tie at Stamford Bridge with just a single league defeat to their name under Thomas Tuchel.
Meanwhile, Arsenal are facing a first season since the mid-1990s without European football as Mikel Arteta continues to be panned for his tactics in the Emirates Stadium dugout.
Jorginho and Kepa combine for clanger
But in a complete turn up for the books in west London, it was actually Arsenal who took the lead when Chelsea dropped a defensive clanger that you'd ordinarily associate with the Gunners.
And that's because Jorginho almost scored one of the worst own goals ever seen in the Premier League when he almost fired by his own goalkeeper with a wayward back pass.
Had there been a full house at the Bridge, you could guarantee that there would have been a collective intake of breath as the ball started bobbling towards an unguarded goal.
Chelsea vs Arsenal match reaction (Football Terrace)
Arsenal score from terrible Chelsea error
In the end, Kepa Arrizabalaga did enough to keep the pass out of the net, but could only claw the ball into the path of the Arsenal front-line having effectively been thrown under the bus.
Emile Smith Rowe eventually provided the final touch with a sweeping finish in off the post and you can check out the full carnage down below:
Talk about carnage. What was Jorginho thinking?!
Unexpected advantage for Arsenal
And to think, the situation could easily have been even more chaotic for Chelsea if it wasn't for the fact that Arsenal scored because Arrizabalaga shouldn't have been using his hands.
Obviously, when it's a pass from one's own teammate, you can't handle the ball, but Arrizabalaga hardly had a chance when it came to preventing a horrific own goal, so was prepared to take the risk.
In the end, Andre Marriner masterfully played advantage to allow Arsenal to see out the phase of play, duly opening the door for Smith Rowe to cash in on Chelsea's miscommunication.
And it gave Arteta's men an unexpected advantage in a game that many would have already written off a straightforward win for Chelsea, taking their 1-0 advantage into the half-time interval.
In the grand of scheme of things, Tuchel won't be losing too much sleep about an error that could easily have happened to any team, but it certainly won't age well in the damning replays.