Arsene Wenger said it was a case of "job done" for Arsenal as they qualified for the last-32 of the Europa League as Group H winners despite losing in Cologne.
The Gunners had already qualifed for the knockout stages before the game against the German Bundesliga's bottom club at the RheinEnergieStadion on Thursday.
Therefore, it was no surprise when the Frenchman changed the entire starting XI from Saturday's 2-0 north London derby win against Tottenham.
Danny Welbeck played 45 minutes on his return from a seven-game groin injury absence, while Olivier Giroud and Jack Wilshere also started in an XI made up of youth and experience.
We now play our final game at home against Bate Borisov without much at stake, other than the fact that we want to win the game.Arsene Wenger
But, in a lacklustre performance, Cologne came out on top courtesy of a 66th-minute penalty which was converted by Sehrou Guirassy, after Mathieu Debuchy was harshly adjudged to have fouled him in the area.
Wenger felt his side lacked the finishing touch in attacking areas, while he praised the opposition's performance.
"We had a lot of possession," he said. "We lost the game to one shot basically. It was a very nice penalty that we have to take on board. It was honestly not a penalty at all.
"We missed a little bit of the accuracy in our passing in the final-third that is required to score more goals.
"We had plenty of dangerous situations but we always missed a little something to finish our chances.
"I must also say that Cologne defended with spirit, with commitment and overall the crowd was absolutely fantastic for them."
Arsenal sit top of the group on 10 points - four ahead of Cologne and Red Star Belgrade - and face Bate Borisov at the Emirates Stadium in their final game.
On topping the group, Wenger added: "You feel you have done the job to finish top of the group.
"We now play our final game at home against Bate Borisov without much at stake, other than the fact that we want to win the game. It's what we wanted."
Arsenal are 12121/1 to win the Europa League, while AC Milan are priced at 1212/1 and Lazio are available at 1212/1.
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