London - Arsenal's Europa League encounter with Cologne finally got underway an hour late on Thursday despite police making arrests after dealing with "disorder" at the Emirates Stadium as German fans occupied home sections of the ground.
Thousands of ticket-less supporters of German club Cologne arrived at the Emirates, while travelling supporters who did have tickets were unable to gain access to the ground for the Group H opener, with kick-off delayed by an hour in the interests of "crowd safety".
The match did begin at its rescheduled time of 9:05pm local time, having been pushed back an hour from its original 8:05pm start.
Some Arsenal fans called for the Cologne supporters to be moved to designated away areas but stewards decided to leave them where they were, with a club spokesman telling Britain's Press Association: "The players were relaxed and preparing for the game despite the delay... The decision to go ahead was the best option and the safest option."
Cologne fans, who had been singing before kick-off, had even more reason to celebrate when Jhon Cordoba's 40-yard strike gave the visitors a ninth-minute lead.
"Officers are dealing with disorder at the Emirates Stadium where fans have gathered for the Arsenal vs FC Koln match," said a pre-match statement issued by London's Metropolitan Police.
"A policing plan is in place for the game. Additional officers have been deployed."
A subsequent statement confirmed arrests had taken place.
"Arrests at 21:41pm = four people have been arrested on suspicion of public order offences," Scotland Yard said.
One social media post appeared to indicate scuffles inside the ground, with Richard Conway, a BBC sports news correspondent, tweeting: "Koln (Cologne) fans fighting with stewards inside Emirates stadium. Group arrived in home end and fought their way into away section."
Earlier reports suggested as many as 20,000 Cologne fans had gathered in London just hours before Thursday's kick-off despite only 3 000 tickets being made available to away supporters.
Posts on social media sites showed large numbers of Cologne fans singing and marching around Oxford Circus in central London.
Meanwhile Arsenal issued a statement on their website warning travelling fans they risked being kicked out of the ground if they bought tickets in the sections of the Emirates reserved for home supporters.
"Please note visiting supporters that purchase a ticket in the home end for this fixture are likely to be ejected from the stadium," the statement said.
Cologne are currently bottom of the Bundesliga table, having lost all three of their opening games in this season's German top flight.
But they qualified for the Europa League after finishing fifth last term.
Cologne coach Peter Stoeger, asked on the eve of the Group H opener if he had a message for the thousands of travelling fans, replied: "Enjoy the pubs!"
Not suitable for sensitive viewers as video contains strong language.