Indeed, the Gunners host Tottenham in the north London derby at the Emirates Stadium on Sunday afternoon with both sides on form domestically heading into the crunch clash.
And the German has praised their fierce rivals but says their duty is to stop Mauricio Pochettino's men in their tracks.
The Arsenal centre-back told Sky Sports: "Tottenham are always competing for the top spots, always reaching the Europa League. They want the next step into the Champions League spots. Our job is to keep them quiet as much as we can."
It's an interesting way of putting things, of course, and you can imagine an Arsenal player telling his team-mate that everything else can be forgiven as long as you keep Tottenham quiet!
Mertesacker himself was recently identified by pundits as Arsenal's weak link, suggesting Spurs could exploit the German's lack of pace if he plays on Sunday afternoon.
Whatever happens, this is one of the most promising north London derbies for a while. The Gunners are as close to the top of the Premier League as they will ever be, it seems, while Tottenham are unbeaten in the league since the first day of the season.