Alexis Sanchez scored a stunning goal as Arsenal came from behind to beat Cologne in a controversial Europa League match delayed for an hour following crowd trouble.
Chilean Sanchez, who nearly left the club to join Manchester City on transfer deadline day, picked the ball up outside the area and curled a shot past keeper Timo Horn.
The game did not begin until 21:05 BST as thousands of visiting supporters arrived at the ground without tickets and then clashed with stewards inside the Emirates Stadium.
When the match did get under way, Cologne took the lead in spectacular fashion as Jhon Cordoba lobbed fellow Colombian David Ospina from 40 yards.
Striker Olivier Giroud planted a header wide of goal from six yards for the much-changed home side, who were booed at the half-time whistle.
But substitute Sead Kolasinac equalised with a thumping volley before Sanchez struck, and Hector Bellerin then added the third from close range, as midfielder Jack Wilshere made his first appearance for the club since August 2016.
In Group H’s other game, Red Star Belgrade drew 1-1 against BATE Borisov.
Forward Sanchez scored 30 goals in all competitions for Arsenal last season as they won the FA Cup.
But in August, he almost joined former boss Pep Guardiola at Manchester City for £60m, but the Gunners pulled out of the deal after failing to find a replacement.
Sanchez made his second start of the season in an impressive showing, capping his performance with a sublime effort in the second half – his first goal of the season.
He could have scored another two, but struck a free-kick straight at Horn and shanked wide from inside the area.
Forgotten man Wilshere, who spent last season on loan at Bournemouth before suffering a broken leg, came on for Alex Iwobi on 68 minutes, and the England international’s clever dummy was instrumental in the lead-up to Bellerin’s goal.