Sead Kolasinac and Alexis hit stunning second-half strikes to win us a game that was delayed for an hour by crowd safety issues.
It hardly seemed worth the wait when a piece of individual brilliance from Jhon Cordoba caught us out in the 10th minute.
David Ospina rushed out to clear from outside his box and, when the ball was knocked back into Cordoba’s feet, he had the presence of mind to spin and launch a shot from 40 yards that sailed over the retreating goalkeeper and into the net.
That setback - and the noise being generated by the Cologne fans - made this feel like an away match at times. But having carved out half-chances in the first half - mostly through Olivier Giroud headers - we turned the screw after the break.
Kolasinac’s half-time introduction and a switch to 4-2-3-1 paid immediate dividends when the Bosnian lashed home a volley after Theo Walcott’s attempted cross had flicked up off a defender.
Cologne, having looked neat and tidy early on, were now retreating. And Alexis, too deep to do damage in the first half, increasingly found himself in dangerous positions.
He made it count. Chasing the ball down on the left touchline, Alexis dribbled inside, evaded two defenders and worked himself just enough space to curl a sumptuous shot inside the far post. The keeper barely moved.
Jack Wilshere came on seconds later - a year and 14 days after his last first-team appearance - and received one of the biggest cheers of the night.
Hector Bellerin added some gloss to the win, showing desire to reach a rebound first and fire past Timo Horn after Walcott’s shot had been saved.
A delayed start, then a false start… but a happy ending to our Europa League debut.
AS IT HAPPENED
WHAT IT MEANS
A 1-1 draw between Red Star Belgrade and BATE Borisov means we top Group H by two points after one game. Our next Europa League fixture is in Belarus against BATE Borisov on September 28.
We travel to Chelsea on Sunday for our fourth game against the Blues in four months. We beat them twice at Wembley - in the Emirates FA Cup final and Community Shield - and lost in China in pre-season.
Our next visitors to Emirates Stadium are Doncaster Rovers in the Carabao Cup on September 20.
CHASING A CENTURY
Giroud went into the game on 99 goals for the club… and ended it on 99.
Nonetheless, the France striker was our most dangerous player in the first half, going close a number of times:
10 - Alexis clips in a free-kick and Giroud climbs well to power a header towards the top corner. The keeper claws it away; the flag is up anyway.
13 - Ainsley Maitland-Niles delivers a cross and Giroud mades a trademark near-post run… but he’s blocked off.
20 - A flowing move sees Alexis pick out Walcott, who leaves the ball to run to Bellerin. He swings in a cross from deep and Giroud gets up to generate plenty of power in a header that Horn saves.
25 - Alexis curves a ball into Giroud’s path and he tries a flick to take it past his marker. It doesn’t quite come off.
39 - Another cross, this time from Alexis, prompts another good leap from Giroud. This time he heads wide under pressure.
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