Arsenal came from behind to see off the challenge of Koln and secure their first victory in the Europa League with an impressive second half performance at the Emirates.
The German club started quickly, taking the lead with a stunning Jhon Cordoba strike inside ten minutes. And for much of the first 45 minutes, they successfully restricted a lacklustre Arsenal outfit.
But after half-time, the home side significantly upped their game, goals from substitute Sead Kolasinac, Alexis Sanchez and Hector Bellerin securing an ultimately comfortable win.
After an hour-long delay due to crowd trouble, the game finally began at a high tempo, the atmosphere heightened by the events prior to kick-off and the enthusiasm of the raucous away supporters.
And it was the visitors that were celebrating first, a superb, audacious strike from Cordoba sailing over the head of David Ospina, who had rushed off his line in an attempt to clear the ball.
It was not an undeserved lead for Koln. The side sitting bottom of the Bundesliga had started with assurance and pugnacity, and kept Arsenal comfortably at arm's length.
The Gunners, other than an Olivier Giroud header and Theo Walcott mis-hit, struggled to find any notable openings, a much changed, second-string side lacking in creativity and composure.
By half-time, Koln remained relatively comfortable, while Arsenal were left frustrated and perhaps somewhat surprised by the effectiveness of their opposition.
There was far more urgency about Arsenal after the break, and they were immediately rewarded. Kolasinac, on moments earlier to replace Rob Holding, met a blocked Theo Walcott cross with a fiercely struck volley that left Timo Horn helpless and arrowed into the bottom corner.
After the ponderous, lethargic first-half display, Arsene Wenger's side appeared to be reinvigorated, ready to assert their control on Koln, who for the first time looked stretched.
They were very nearly ahead just after the hour mark when Ainsley Maitland-Niles drove into the box, skilfully evading challenges, but saw his progress halted by the outstretched arms of Horn.
But minutes later, they were in front. Sanchez, naively given time and space on the edge of the box, cut inside and curled a delightfully accurate shot into the far corner.
The hosts had impressively stamped their authority on the second half, although the lively Cordoba offered a reminder that the game was not yet decided, testing Ospina with a driven effort towards the near post.
The points were sealed, however, with ten minutes remaining, when Bellerin followed up a saved Walcott shot to score Arsenal's third of the evening and finish the challenge of the commendable visitors.