Jordi Gomez waited several minutes to hammer home his penalty - which he did with aplomb.
But Arsenal dug deep. They broke face, and went with two big men up top, and in the end Mertesacker made amends for his earlier error and equalised.
Arsenal went on to win the penalty shoot-out with relative ease and are now on their way to Wembley - againa
In respect to Arsenal this was a tough game. Wigan have proven themselves to be a tough opponent in this competition - don’t believe me, ask Manchester City.
And Arsenal are not exactly at a full complement right now.
They have an abundance of injury woes to consider - with Jack Wilshere, Abou Diaby, Laurent Koscielny, Tomas Rosicky all out and of course their club record signing - Mesut Ozil.
He has been out since the second leg of the Bayern Munich Champions League tie with a hamstring problem - although is expected to get back into full training very soon.
However, sitting on the medics table has not let him forget his team-mates.
He was on the Tweet this evening supporting his mates in action - and at the end of it all was left as happy as any other Arsenal fan.
And he might just get to go to Wembley this season after all…
Yessss merte— Mesut Özil (@MesutOzil1088) April 12, 2014
Come on gunners— Mesut Özil (@MesutOzil1088) April 12, 2014
Finaleeeeeeeeee— Mesut Özil (@MesutOzil1088) April 12, 2014
Well done AFC— Mesut Özil (@MesutOzil1088) April 12, 2014
Arsenal Never gives up. Thanks Per, Thanks guys. You made my Day.— Mesut Özil (@MesutOzil1088) April 12, 2014