Four people were arrested on suspicion of public order offences before Arsenal’s Europa League opener against Budesliga side Cologne at London’s Emirates Stadium on Thursday.
The match, which was originally scheduled at 20:05 BST, was delayed by an hour “in the interests of crowd safety”.
Thousands of ticketless away supporters turned up outside the ground and there were some scuffles between fans and stewards inside after the gates opened, the BBC reported.
The German side, playing their first European match in 25 years, had only been given a ticket allocation of 2,900 but around 20,000 of their fans brought central London to a standstill earlier on Thursday afternoon.
Report said that a group of Cologne fans entered the Emirates Stadium adjacent to the away section and proceeded to fight with stewards in an attempt to gain entry to the away section. Police wearing riot helmets – some with dogs – then entered the stadium and order was restored.
The Metropolitan Police said in a statement: “Officers responded to reports of disorder at the Emirates Stadium earlier this evening where fans gathered for the Arsenal vs FC Koln match. A policing plan was in place for the game and additional officers were deployed.”
The match was held smoothly without reports of trouble and Arsenal won 3-1.
Cologne took full advantage of Arsenal’s dozy start and it was keeper David Ospina who was at fault.
It came in the ninth minute when the Colombian keeper rushed off his line to make a sweeper-style clearance.
The clearance went straight to Leonardo Bittencourt, bouncing off the midfielder to pick striker Jhon Cordoba, who chipped from 35 yards over the head and out of reach of Ospina and into his unguarded net.
Sead Kolasinac came off the bench and scored the equaliser in the 49th minute.
Walcott tried to cross from the left, but his ball bounced off Lukas Klunter and found Kolasinac, who volleyed home a powerful shot with his left foot.
With Jack Wilshere about to emerge from the bench for his first Arsenal appearance in 13 months, Sanchez struck the decisive blow.
The Chilean cut in from the left, drifted past two defenders and curled a beauty inside the far post.
Hector Bellerin made sure of the result late on after scoring from Walcott’s rebounded shot ten minutes from full-time.
Arsenal’s Europa League clash with Cologne descended into chaos last night as 20,000 German fans invaded the Emirates.
About 20,000 fans were estimated to have made the trip from Germany to savour their club’s first taste of European football for 25 years.
There were reports of anti-social behaviour, including supporters urinating in the streets. One photograph on social media showed a man with blood pouring from a head wound.
ITV political editor Robert Peston reported Nazi salutes and ‘peeing on doorsteps’ by Cologne fans amid ‘chaos at Arsenal’. Witnesses said stadium seats were vandalised.
Wenger said: ‘We waited patiently. At one stage I thought we will not play. I couldn’t see the police taking any risk. We live in a society of 100 per cent security. I thought they would not take a gamble when we saw the scenes around the stadium. Our supporters dealt well with the situation.
‘What was difficult for me were all plans to think about. Do we play tomorrow? What time? Or next week, but they had a Bundesliga game and we had a League Cup game, so do we move that to Tuesday and play on Thursday? All kinds of things. If nothing now happens after the game then yes, it was the right decision to play.’