Alexis Sanchez's fine strike helped Arsenal to a 3-1 win over Cologne in Thursday night's Europa League Group H tie, after the match was delayed by an hour for crowd safety reasons.
The match was postponed until 9.05pm 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.
Cologne, playing their first European tie in 20 years and first in this competition since 1992, have lost their opening three Bundesliga games, but took the lead in bizarre fashion early on.
Theo Walcott fluffed a chance later in the first half from 12 yards, but Arsenal equalised on 49 minutes through defender Kolasinac, who rifled home a volley from the left of the box as Walcott's cross looped up from a deflection.
Ospina's tame clearance from a long ball was touched forward by Leonardo Bittencourt, allowing Cordoba to take aim from 40 yards, finding the corner of the net over the hapless Arsenal goalkeeper.
Sanchez, whose much-talked-about move to Manchester City broke down late in the summer window, hit a superb strike into the top corner from 20 yards with 23 minutes remaining, leaving Timo Horn helpless.
Bellerin made it 3-1 late on, finding the bottom corner from an angle after Walcott's effort had been well saved by Horn.
Opta stats
- This was Arsenal's first European match outside of the Champions League (incl. qualifiers) for the first time since May 2000 - 17 years and 120 days ago.
- Cologne lost a competitive game that they were winning at half-time for the first time since December 2014 (1-2 v Augsburg).
- Arsene Wenger has now registered a win over 57 different clubs during his tenure as Arsenal manager (from 64 different teams faced).
- Alexis Sanchez scored his first goal in the UEFA Europa League, in what was his 10th appearance in the competition (nine for Udinese, 1 for Arsenal).
The manager
Arsene Wenger: "I believe we had a little bit of a slow start, our combinations were too slow, and we were shocked they scored.
"In the second half I believe our team was better balanced better equipped going forward. Second half was one-way traffic, just a question of time, overall I think we won it in a convincing way.
"We moved to a four in the second half, Kolasinac gave us a lot going forward, and pushed Sanchez forward, he played deep in the first half. When he had more support he looked good."
Man of the match - Hector Bellerin
Sanchez may have stolen the headlines with a fine hit, but Spaniard Bellerin was the real class act on what could have been a hairy night for Arsenal.
The hosts struggled in their three-man defence in the first half but looked far more solid after the break, with Bellerin ushering out Cologne attacks on numerous occasions, while providing a threat down the right wing.
He showed his usefulness in the opposition box late on, reacting fast to score a deserved third. They'll want him fresh for Super Sunday.
What's next?
Arsenal now go to Stamford Bridge to face champions Chelsea on Super Sunday, live on Sky Sports Premier League at 1.30pm, while their next Europa League clash comes away at Belarus' BATE Borisov on September 28.