Mertesacker's header at the end of the first half proved enough to secure a 1-0 win at Fulham - where both sides finished with 10 men after Gunners' striker Olivier Giroud saw red in the closing moments. It was a ninth win in 12 league games for the Gunners, who are in third place, a point ahead of Chelsea and two clear of Tottenham although both have played a match less.
That record, though, will be severely tested next weekend, when United head to the Emirates Stadium, and Koscielny said: "I hope we can keep Robin quiet. He is a good player. I enjoyed my time playing with him, but I hope we keep the story with us."
The France defender said: "It will be a hard game for the whole team, but we are at home and we will try to get the three points. It will be a good game against a big team and I think they have won the title (already)."
Koscielny, 27, has formed a good understanding alongside Mertesacker, whose close-ranger header just before half-time proved enough for victory over a battling Fulham side. So much so that it has kept captain Thomas Vermaelen on the bench.
France international Koscielny believes the 6ft 7in German provides a steady influence at the heart of the Arsenal rearguard.
He said: "We play well together as a pair. We communicate on the pitch well.
"His experience is vital and it helps us work together on the pitch, so we try and talk to each other a lot and it is important at the back to have an understanding."
Koscielny added: "Per is a very good player. He reads the ball well. He is clever, attacks the ball and wins headers whereas I can go behind and be quick and cope with the long balls.
"He is good technically so he is good for the defence. Per is calm on the pitch. He is good for me, he uses his experience, this helps me, and he helps the team."