The Gunners were 1-0 victors at Craven Cottage thanks to a first-half header from the German, whose form at the other end of the pitch has been keeping club captain Thomas Vermaelen out of Arsene Wenger's starting line-up.
Koscielny believes that Mertesacker's ability to read the game and stay calm under pressure is helping the pair develop a strong understanding.
|10/3||Arsenal's match against Manchester United is 10/3 with BetVictor to be a score draw
"We play well with Per, we have good communication on the pitch and try to talk a lot. Per is calm on the pitch all the time and that's good for my experience."
The 27-year-old revealed that Olivier Giroud was disappointed in the dressing room after failing to score for a second successive game before receiving his marching orders for a "poor tackle" late on.
"Yeah, he was sad – he can't play against Manchester United," Koscielny noted of his countryman. "It's normal, he's human and he wants to score more goals for the team. He works hard but he's human, he made a poor tackle."
The France international also admitted that the squad are relishing Sunday's clash with league leaders Manchester United, where they will be tasked with shackling former captain Robin van Persie.
"I hope [I can keep Van Persie quiet], he is a good player," Koscielny continued. "It will be a hard game for both teams but we will want the three points. It will be a very good game against a big team.
"We are a squad and we want to be strong for the team as we want to qualify for the Champions League."