Choas inside the Emirates led to the Europa League tie between Arsenal and Cologne being delayed by over an hour.
The match began at 9.05pm as away supporters managed to gain access to seating allocated for home fans.
Around 20,000 Cologne supporters arrived in London, despite the German club being given a ticket allocation of 2,900.
The game managed to go ahead without much crowd trouble but it is believed the tourists bought tickets through touts and other means to enter the stadium in sections reserved for home fans, causing concerns over security.
It was the first time in 25 years Cologne has played in a European competition.
Arsenal came from behind to win 3-1.
In the other Europa League tie featuring an English side, Everton were roundly beaten by their Italian hosts Atalanta 3-0.
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