Neal Maupay’s late header condemned mediocre Arsenal to a 2-1 defeat at the hands of Brighton and Hove Albion.
Adam Webster’s first-half strike gave the daring visitors a well-earned lead at the interval, before Alexandre Lacazette levelled shortly after the break.
David Luiz then saw a volley ruled out for offside before Maupay’s late header handed the Seagulls all three points.
And the defeat left the hosts without a win in nine while handing Brighton their first ever win at Arsenal.
Brighton youngster Aaron Connolly had the first real effort of the opening half, cutting inside from the left and curling straight at Bernd Leno on 17 minutes.
The Republic of Ireland international, who burst onto the scene with a blistering two-goal Premier League debut against Tottenham in October, was a menace all night against another north London side.
Just 19, he showed his intent once more when he forced Hector Bellerin into fouling him a fraction short of what would have been a penalty.
Arsenal, without a win in their eight prior matches, looked shaky throughout the first half while the visitors looked the more composed outfit.
That proved quite surprising, considering Brighton themselves entered the match three points worse off than they were at the same mark last season - a season which ended in a relegation scrap.
But Webster saw a header saved by Leno before Maupay almost opened the scoring with a hammered effort across goal - which Connolly missed by fractions at the far post.
Pierre-Emerick Aubameyang then slotted an effort fractionally wide in a rare opportunity for the hosts, but Brighton went close again when Maupay tested Leno from the edge of the box, before Davy Propper did similar.
Graham Potter’s men finally did make the breakthrough nine minutes before the break. Dan Burn headed the ball back across goal, Connolly touched it down and Webster slammed home from close range.
The rest of the half predominantly belonged to the visitors. Twice the Seagulls broke in numbers and should have found a second but for two weak final passes.
Between those chances, though, Joe Willock was kept out by a terrific Mat Ryan save. Aubameyang’s lobbed cross found the youngster unmarked, only for the Australian to kick his headed effort away.
It was a familiar atmosphere at the Emirates and interim manager Freddie Ljungberg threw on the club’s record signing, Nicolas Pepe, in a bid to improve Arsenal’s fortunes.
The substitution proved the perfect remedy for the lethargy around the ground, with Pepe looking lively before a 50th minute equaliser from Lacazette, who flicked a header into the far post from a Mesut Ozil corner.
Connolly again might have handed Brighton a goal when he was played into space by Maupay, but instead of picking out team-mate Aaron Mooy, he saw his effort blocked for a corner.
Full backs Bellerin and Sead Kolasinac then took turns in firing crosses into the six yard box, both which fractionally missed the lurking Aubameyang.
Potter’s side might have struck again when Steven Alzate’s chipped cross was diverted to Maupay with Mooy’s header, but the Frenchman was denied by a wonderful Leno save.
Just after the hour mark, Arsenal thought they had taken the lead when Luiz volleyed a free-kick into the roof of the net - only for VAR to correctly deem the Brazilian offside.
Alzate then had to be quick on his feet to block Aubameyang after Lewis Dunk conceded possession in midfield, before Ozil’s half-volley landed comfortably wide.
Just as things started to look hopeful for Arsenal, though, Brighton struck.
With ten minutes remaining, Mooy beat Bellerin and curled a delightful cross onto Maupay, who flicked a header into the far post.
Pepe then fired an effort at Ryan in an attempt to level, before second-half substitute Gabriel Martinelli looked to have succeeded before the Australian tipped his header behind at the last moment.
The result left Ljungberg without a win in his opening two matches as interim boss as the Gunners continue their hunt for a manager to replace Unai Emery.
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