Police with dogs were deployed inside the stadium after scuffles broke out between away fans and stewards as authorities struggled to deal with up to 20,000 German fans arriving for a game where Cologne had an official allocation of just 3,000.
Problems started when non-ticketed supporters blocked access for those trying to get into the game and were exacerbated when a gate was rushed, allowing a flood of supporters into the game.
One of the main access walkways had already been shut off two hours before the game and the decision was made to keep fans out while checks were made and the stadium cleared for a more orderly admission of fans.
Even then, thousands of Cologne fans were clearly cheering on their side from within home areas, but the decision was taken that it would be safer to allow the game to proceed rather than try to allow the fans to disperse into the streets around the stadium.
UEFA will demand a full report into the problems but Arsenal head of communications Mark Gonnella said: “We decided the safest option was for the match to go ahead. We let fans into the stadium as everything was under control.
“We were aware about large numbers of fans coming and tried to avoid a situation where there would be large numbers of supporters without tickets.”
Despite the hour delay, Arsenal were able to get the job done against the German outfit - just.
Arsenal were in full control from the beginning and looked likeliest to open the scoring.
But it was the Cologne fans who were jumping around in jubilant celebrations after a stunning goal from Jhon Cordoba.
David Ospina came way off his line to clear a long ball over the top but his miscued kick fell nicely for Cologne before the ball was played into Cordoba who struck a looping shot over the back-tracking goalkeeper from 40 yards out.
And the Gunners struggled to break down Cologne for the remainde of the half as their fans began to grow restless.
Their groans were quickly appeased soon after the break though after Saed Kolasinac, coming on as a substitute at half-time, equalised with a thumping finish.
And Alexis Sanchez proved how invaluable he is Arsenal with a sensational strike from the edge of the area to give them the lead for the first time in the night.
And Hector Bellerin completed the scoring in the 81st minute when he poked home after Theo Walcott's shot was saved.
Source: Daily Express