Arsenal suffered their first Europa League defeat of the season as Cologne kept their qualification hopes alive with a 1-0 victory on Thursday
The Gunners, who had already qualified for the knockout phase, needed just a point in Germany to secure their passage into the next round as group winners
But Sehrou Guirassy won and then converted a contentious penalty on 62 minutes to deny Arsene Wenger's second-string, as Cologne boosted their hopes of following the Gunners into the next round
However, there was a positive end to a disappointing night for Arsenal, as Red Star Belgrade's draw with BATE Borisov ensured they would finish top of Group H
Ainsley Maitland-Niles called Timo Horn into action inside two minutes at the RheinEnergieStadion, but his opposite number, the returning David Ospina, was soon busy as he tipped Jhon Cordoba's drive behind
Francis Coquelin then flashed a fierce drive inches wide of the target before rattling the frame of the Cologne goal with another sweetly-struck effort on the half hour
Danny Welbeck's return lasted 45 minutes as Alex Iwobi, tasked with igniting a stale contest, entered the fray at the interval
But Wenger's hopes of strolling into the round of 32 as group winners suffered a blow as Mathieu Debuchy was penalised for a foul on Guirassy, and the 21-year-old dusted himself down to coolly convert from 12 yards
Gunners captain Per Mertesacker came close to levelling the contest immediately but Horn was on hand to claw his header off the line, and the Cologne stopper was in similarly impenetrable form to deny Jack Wilshere's fizzing drive
Substitutes Reiss Nelson and Eddie Nketiah both had late chances before Wilshere was denied by Horn again as Arsenal were left to turn their attention to their final group game against BATE in two weeks
With Cologne's long-awaited return to European football on the cusp of petering out, Guirassy was the man who made the difference
 The 21-year-old won and converted the decisive penalty which kept Cologne's Europa League campaign alive heading into the final group match, and finally gave the passionate home faithful something to cheer about after a season of torment
Arsenal resume their Premier League campaign with a trip to Burnley at 2pm on Sunday
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