Arsenal came from behind to beat Cologne in their delayed Europa League opener against a backdrop of crowd trouble at the Emirates Stadium.
Kickoff was delayed by an hour as ticketless away supporters attempted to enter the ground, with plenty of Cologne fans sat in among the home section when the tie finally got underway in a match the Gunners eventually winning 3-1.
Four arrests were made on suspicion of public order offences as extra police were deployed to the scene.
On the pitch, Arsene Wenger's much-changed side showed determination to fight back from Jhon Cordoba's early 40-yard strike and seal three points.
It was only after the interval, following the introduction of Sead Kolasinac and a change of shape, that the Gunners hit back.
Kolasinac levelled less than four minutes after coming off the bench and Alexis Sanchez, a surprise starter ahead of a trip to Chelsea on Sunday, scored a marvellous solo goal before Hector Bellerin secured the win late on.
The game was placed in doubt as a one-hour delay was announced due to crowd safety concerns and there are plenty of questions to be answered by Arsenal as to how the situation was able to unfold as it did.
Problems were all-but a certainty as some 20,000 Cologne supporters took to the streets of central London hours before kickoff.
The tense atmosphere inside the ground was tested in just the ninth minute as Cordoba gave the visitors the lead with a long-range strike.
David Ospina, starting his first Arsenal game since the FA Cup final, burst from his goal-line to clear but could only find Leonardo Bittencourt with a poor clearance, leading to Cordoba lobbing an inch-perfect drive over the retreating goalkeeper.
Arsenal -- showing as many as nine changes from Saturday's win over Bournemouth and with the disruption of the delayed kickoff -- were slow to get going.
Theo Walcott burst through but could not make telling contact with his shot, with only tame Olivier Giroud and Nacho Monreal efforts testing Timo Horn in the visitors goal before the interval.
Wenger reacted by introducing Kolasinac for Rob Holding at the break, changing his formation in the process, and it paid immediate dividends.
Walcott collected a through-ball but was forced wide and when his deflected cross fell towards Kolasinac, the Bosnia-Herzegovina international rifled home to level.
Sanchez had cut his now-regular pose of a frustrated player but he too had been unable to influence proceedings.
That was until he took the game by the scruff of the neck, cutting inside and finishing with aplomb from the edge of the box to put Wenger's men in front.
Jack Wilshere came off the bench soon after to make his first Arsenal appearance in 383 days, before Bellerin wrapped up the win -- following up from Walcott's saved effort to tuck away just his fifth Arsenal goal.
A draw between Red Star Belgrade and BATE Borisov in Serbia means Wenger's side take an early stranglehold of Group H -- but there are likely to be ramifications following developments off the pitch.