Crystal Palace hammered Arsenal and piled more pressure on Arsene Wenger.
Goals from Andros Townsend, Yohan Cabaye and Luka Milivojevic condemned the Gunners to a humiliating defeat in south London.
And things will only get worse as the inquest rolls on after a gutless, dreadful performance from the visitors.
Wilf Zaha shone again for the hosts, who dominated and deservedly saw off a pitiful Arsenal display.
But what did we learn?
1. Arsenal stuck on repeat
After the 2-2 draw with Manchester City, followed by their 3-0 victory over West Ham, there was a growing sense that the Gunners might yet still be able to secure a place among the top four. But tonight's woeful performance reaffirmed everything wrong with this Arsenal side.
Leadership was lacking across the field while the vast majority of Wenger's men appeared to be afflicted with a crippling lethargy that saw them struggle for ideas and creativity. Wenger has stood poised in recent weeks to recommit his future to the club but there's no doubt that the Frenchman is running out of ideas. If tonight is anything to go by, a fresh overhaul is desperately needed across the club - both on the pitch and off it.
2. Meek Arsenal overpowered in the first half
Crystal Palace didn't even fly out of the blocks in this one, they just played like the superior team from the outset and grew into the game.
Arsenal allowed them to. Perhaps Granit Xhaka and Mohamed Elneny aren't the midfield two needed to control a game in the Premier League, because they've certainly not seemed like it so far and they were dominated by Jason Puncheon, Luka Milivojevic and a half-fit Yohan Cabaye at Selhurst Park.
Without those two purring, the attack failed to get going in any cohesive sense, though still created a handful of chances through individual brilliance.
It's been said many times that the Gunners can't get Santi Cazorla back soon enough. Overrun, out-fought and beaten to every ball, it was seriously uninspiring stuff.
Arsenal have the same season every year
Arsenal have the same season every year
1/8 Surprise early defeat
A surprise early defeat, such as 2013/14's to Aston Villa or 2015/16's to West Ham United, makes July's Emirates Cup win seem like a distant memory.
2/8 Impressive win against top club
A promising win against a title rival, like last season's 3-0 victory over Manchester United or this season's win over Chelsea, has the Emirates hoping for the best again.
3/8 Injuries start to mount up
However, a long queue starts to form outside the treatment room. Key players, as well as regular absentees, tend to be the victims.
4/8 November curse strikes again
Arsene Wenger's side then begin to unravel in November, with the curse kicking in after an away defeat against one of the top flight's lesser lights. It's around now that the already-faint hopes of a title challenge start to fade.
5/8 Champions League elimination
The most predictable part of it all comes in February, with Champions League elimination, usually to Bayern Munich, Barcelona or Monaco, if they are really unlucky.
6/8 Title hopes finally killed off
A heavy, signature defeat to a fellow top six side puts paid to any lingering hopes of a title challenge in late February or March. 2013/14's 6-0 reverse at Chelsea, Arsene Wenger's 1,000th game in charge, is perhaps the most memorable example.
7/8 Strong rally to finish
The pressure is off, time to turn the style on. A rally at the tail end of the season does wonders for Arsenal's league standing, but little to combat allegations of flakiness.
8/8 Top-four finish
Arsene has his 'trophy'. Champions League football is coming to the Emirates again next year. What more could the fans want?
3. Mesut Ozil disappears
Mesut Ozil has been accused of going missing in the big games, but this was a case of the German being conspicuous by his absence in a match against one of the Premier League's more unfashionable sides.
There are, it seems, two very black-and-white camps in which people find themselves. Either Ozil is a genius and you are a philistine for not appreciating that, or he is a lightweight fraud who is stealing a living.
The truth, as ever with these binary things, is somewhere in between but there is one thing that is certain - Ozil had a quiet night. Even with Palace missing first-choice defenders James Tomkins, Scott Dann and Patrick van Aanholt, the German international failed to make an impression on a backline playing only its second game as a unit.
4. Zaha and Benteke are becoming a fearsome strike pairing
Wilfried Zaha and Christian Benteke have become a strike partnership in Sam Allardyce's rough 4-4-2 at Palace, and they are becoming one of the most disruptive duos in the league.
When Benteke is on sledgehammer form like today he becomes a nightmare for opposing centre-backs, occupying both and dragging them all over the field. Zaha's pace and trickery make him a match-up nightmare too, so when he drifts around to find one-on-one situations it invariably gives his side a chance of making something happen.
Today both were firing and, working in tandem, gave Shkodran Mustafi and Nacho Monreal a game to forget.
Zaha has shrugged off accusations that he doesn't have an end product by becoming a more productive player than Mesut Ozil or Raheem Sterling this season. Two more assists today help massage those totals further.
5. Twinkle-toes Townsend shines
With his ability to make something out of nothing, Andos Townsend was quite simply magical at times on Monday night. Twisting and turning to worm his way past a shambolic Arsenal defence, the winger caused no end of troubles for the visitors on the left. Even Hector Bellerin struggled to contain him.
His goal was well-judged, arriving right on time to meet Zaha's cut-back and fire the ball into the back of the net. The player looked confident throughout, too, and wasn't afraid to try his luck with a number of audacious shots on goal - even if many of them failed to find target. Alongside Zaha and Benteke, he was one of Palace's stand-out places and helped guide them to a memorable victory at Selhurst Park.Reuse content