Alexis Sanchez's fine strike helped Arsenal to a 3-1 win over Cologne in their Europa League Group H tie, after the match was delayed by an hour for crowd safety reasons.
The match was postponed with many home fans unable to enter the turnstiles due to thousands of gathering Cologne fans outside the stadium.
Those fans were celebrating first as Jhon Cordoba gave Cologne the lead after 10 minutes, superbly lofting the ball over David Ospina from 40 yards after the goalkeeper's weak clearance.
Arsenal levelled after the break through Sead Kolasinac's fierce left-footed volley, just four minutes after being introduced at half-time.
But Sanchez put Arsenal ahead on 67 minutes with a fine curling effort into the top corner from the edge of the box, his first goal of the season.
Hector Bellerin rounded off the win (82), finishing up on the rebound from Theo Walcott's initial effort.
As kick-off approached, it was clear there were many groups of visiting supporters in home sections of the ground, with reports of up to 20,000 Cologne fans in London on Thursday.