The pressure on Arsenal manager Unai Emery intensified as Daichi Kamada's brilliant double earned Eintracht Frankfurt victory at the Emirates Stadium.
The Gunners boss came into this Europa League match having failed to lead his team to victory in their previous six outings, and this latest defeat means this is their longest winless run since February 1992.
At full-time the Spaniard appeared to make a gesture to the sparse home support as they jeered him, with some holding 'Emery Out' posters having watched their side surrender control against a team who were a clear second best in the first period.
However, Arsenal will seal qualification for the last 32 if they avoid a heavy defeat at Standard Liege in their final Group F game.
It looked like the Gunners had turned the corner after they dominated the opening period. Eintracht spent most of it trying to keep Arsenal's attack at bay until Pierre-Emerick Aubameyang made the breakthrough with a strike just before half-time.
The Bundesliga side only managed one shot on goal in the first half, but were transformed after the break and equalised when Kamada curled in a fierce effort from the edge of the box.
The 23-year-old Japan international then put his side in front with another sweet strike from the edge of the area.
The contest also marked the return of Granit Xhaka to the Arsenal XI. The Swiss midfielder had missed the Gunners' past five matches after his infamous substitution in the 2-2 draw against Crystal Palace at the end of October, when he angrily gestured to supporters.
The 27-year-old appeared to pick up a knock to the knee in the first half but following treatment played the full 90 minutes.
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The Europa League had offered some respite from the difficulties of the top flight - where his side have only won four of their 13 games and are eight points adrift of the top four - but the same problems reared their head on a forgettable night at Emirates Stadium.
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It was all smiles on the home bench in the first half, and the only issue Emery had to contend with was being told he had to change his jacket because it clashed with Eintracht's colours.
Even the 31st-minute departure of the injured David Luiz, who was playing in midfield, did not upset the Gunners' rhythm as the attack of Aubameyang, Joe Willock, Gabriel Martinelli and Bukayo Saka continually troubled the opposition backline.
Martinelli had a shot blocked and header cleared off the line while Aubameyang nodded wide before he swept home the Brazilian's low cross just before half-time.
It was the former Borussia Dortmund striker's 10th in 13 appearances against the Bundesliga club and his 31st goal in 44 home appearances for the Gunners.
However, it was a very different story for the home side in the second half. Two substitutions by Eintracht coach Adi Hutter revitalised their attack, but his players were aided by some poor Arsenal defending.
The lively Kamada was allowed to advance towards the edge of the area by Sokratis before launching a brilliant strike past keeper Emiliano Martínez, and was then given even more space to line up his second, which found the same corner.
That was the 18th goal conceded by Arsenal in nine games. The home attack, so potent in the first half, failed to find a response in the closing minutes as Eintracht defeated English opposition away from home for the first time since beating Burnley 2-1 in the Fairs Cup in April 1967.
Perhaps Xhaka will have been relieved that the attention was shifted from him onto his manager. He produced a competent display in front of his backline, although perhaps could have done more in helping defender Sokratis close down Kamada for his first goal.
The injury to his knee in the first half did not appear to have affected his overall performance and he even raised a cheer from the home support when he tricked his way past an Eintracht defender to set up Calum Chambers, who fired over the bar.
The only stain was the late yellow card he picked up for dissent when he threw down the ball in frustration thinking he won a tackle cleanly.
With the injury to Luiz it could be that Xhaka retains his place for next Sunday's trip to Norwich.