Arsene Wenger's team trailed to Jordi Gomez's second half penalty and were just eight minutes away from suffering an embarrassing defeat against their Championship opponents in Saturday's semi-final at Wembley.

But Germany centre-back Mertesacker stooped to head in Alex Oxlade-Chamberlain's scuffed shot and the Gunners held their nerve to win the penalty shoot-out 4-2 following the 1-1 draw after extra-time.

Lukasz Fabianski was the hero as he saved Wigan's first two penalties, turning away efforts from Gary Caldwell and Jack Collison, while Mikel Arteta, Kim Kallstrom, Olivier Giroud and Santi Cazorla all converted to send the Gunners through.

The north Londoners, whose last trophy came in the 2005 FA Cup, will now face Hull City or Sheffield United in the final on May 17 and can spend the next few weeks focused on the battle to qualify for the Champions League.

This was an unconvincing display from Arsenal for long periods, but following a period of disappointing results, Mertesacker hopes the gritty way his team ground out victory provides a much-needed morale boost.

"In the first half we were a bit timid. In the second half I think we hit the post twice and had a couple of chances so it was a good comeback," Mertesacker, who had conceded the penalty which Gomez converted, told ITV.

"I think we have great character, even though a lot of people have questioned that."

Arsenal's Swedish midfielder Kallstrom, who came on in extra-time, insisted the result was all that mattered given his club's struggles of late.

"It was a really tough game, They defended really well but we pushed all the way through," Kallstrom said.

"The semi-final is all about winning. It was tough but we did it. We had to stay strong mentally and at 1-0 down it gets tough. We were focused and even though it was on penalties, we will take it.

"We have been struggling in recent weeks but you have to deal with that, it's part of the game.

"Hopefully, it's a great boost of confidence for the rest of the season."