With the protests of their fans ringing in their ears, Arsenal 's mood was worsened as Bernd Leno's dismal blunder gifted Everton a 1-0 victory at the Emirates.
The Gunners goalkeeper let Richarlison's cross through his legs, diverting it into the back of the net to hand the Toffees the winner in the 76th minute.
Although Arsenal had the lion's share of possession and shots, Everton were the more threatening of the sides throughout the match.
Richarlison had the best chance of the first half and forced an excellent save from Leno with a powerful bottom corner-bound shot.
Gylfi Sigurdsson also went close for the Toffees, whipping a free kick against the crossbar shortly before the interval.
In the second half, Everton were fortunate to avoid conceding a penalty after Richarlison fouled Dani Ceballos in the area, only for VAR to deem Nicolas Pepe was offside in the build-up.
The Brazilian forward then redeemed himself at the other end of the pitch, dancing past Granit Xhaka and forcing a horrible, uncharacteristic mistake from Leno to snatch all three points and boost Everton's hopes of Champions League qualification.
Here are five talking points from the Emirates.
1. Arteta's ineffectual tactical tweak
Since making the gradual move away from a five-man defence, Mikel Arteta has rarely deviated from his tried-and-tested 4-2-3-1 formation this season.
But there was a noticeable change to Arsenal's shape against Everton, with Thomas Partey operating as the sole defensive midfielder in a 4-3-3 set-up.
His colleagues in the centre of the park – Dani Ceballos and Emile Smith Rowe – were given the license to press as high as the Everton defence and support Eddie Nketiah in attack.
This fluid system also saw Nketiah drop deep to collect the ball, while Smith Rowe and Bukayo Saka regularly exchanged positions on the right.
Arsenal's emphasis on attack and intricate passing made for some pleasant viewing, but ultimately they were unable to find a way through their visitors, who were without doubt the more threatening side due to their speed on the break.
2. Nketiah unconvincing
With Alexandre Lacazette injured and Pierre-Emerick Aubameyang recovering from malaria, Eddie Nketiah was handed his first Premier League start since December for the visit of Everton.
The Englishman came into the match full of confidence after netting a late equaliser against Fulham last weekend, and was full of endeavour and movement.
But in many ways he typified Arsenal's performance, producing some nifty bits of skill and trickery while failing to truly threaten Jordan Pickford's goal.
Nketiah made way for Gabriel Martinelli late on and the young Brazilian's direct approach instantly increased Arsenal's attacking intent
3. Pepe's millimetre moment
Another game, another frustrating VAR incident for Arsenal.
After Dani Ceballos' goal against Fulham was disallowed due to the slightest of offside infringements at the weekend, the VAR official found himself drawing digital lines at the Emirates once again on Friday night.
Ceballos thought he had won a penalty as he drew a foul from Richarlison in the second half, but Nicolas Pepe was found to be beyond the last man by a minute distance.
Jon Moss duly overturned his original decision and awarded Everton a free kick as all those wearing red and white at the Emirates let out a cry of exasperation.
4. Fans make feelings clear
To be frank, what was going on outside the Emirates was arguably more interesting than what was going on inside for much of the match.
Arsenal fans flocked to their stadium well ahead of kick-off to protest against the club's owner, Stan Kroenke.
The American billionaire has a somewhat fractious relationship with supporters at the best of times, and signing his club up for the ill-fated European Super League did little to improve his reputation in north London.
Fans chanted "We want Kroenke out" and held up a host of banners urging him to sell up, while fireworks were heard being let off outside the ground during the match.
And a dismal, self-inflicted defeat for their side adds insult to injury for Arsenal fans deeply upset by their club's ownership.
Read the full story about Arsenal fans' protests here.
5. Everton's European hopes alive
Victory at the Emirates ends Everton's six-match wait for a win in all competitions – a run which stretched back to early March.
Not only that, it also keeps their hopes of finishing in the Champions League spots alive.
Everton are just three points behind fourth-place Chelsea and have six games to make up the difference and secure an excellent achievement.
Arsenal, meanwhile, sit one place and six points behind Everton in ninth, having played one more game than Carlo Ancelotti's side.
But the Gunners may yet qualify for the Champions League by winning the Europa League, and face Villarreal in the first leg of their semi-final next Thursday.
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