For the first time in nearly 20 years, Wenger named three central defenders in the 2-1 win at the Riverside and there was surprise at Wembley when he retained the 3-4-3 formation on Sunday.
Yet Wenger’s gambit paid off – after some initial teething problems – as his side came back from a Sergio Aguero breakaway goal to win 2-1 and continue their manager’s bid for an eighth FA Cup trophy.
It was Wenger’s new-found wingbacks who provided the first, Alex Oxlade-Chamberlain crossing for Nacho Monreal to tap home before Alexis Sanchez scrambled home the winner in extra time.
With 19 minutes left to hold Pep Guardiola’s side at bay Wenger was thankful for a defence with notably more bite and brains than his side had shown in recent months, having conceded three goals in three away games before the switch.
And Wenger admitted that he had had the semi-final “in mind” when he first switched to a back three in the North East.
Asked by Standard Sport what had convinced him to keep the 3-4-3 Wenger said: “First of all that we won the game. That the team got confidence back.
“When you analyse the game you look where did we suffer, where were we good, where do Man City play, can we cope with that? To me, it was positive enough to try it today.”
Wenger is not the first manager to find a back three brings the best out of his side. Indeed it was Arsenal’s 3-0 win over Chelsea early in the season that inspired their FA Cup Final opponents to move to the 3-4-3 with which they steamrollered the Premier League.
But Wenger was not concerned by what might have been if he had ditched the 4-2-3-1 earlier, adding: “No matter what you do, even if you get it right, people say why didn’t you do earlier?
“The opposite is right as well. If you get your starting lineup wrong and change it at half-time people say ‘you see, he’s a tactical magician because he changed it at half-time’. But they forgot he got it wrong at the start.
“You can always judge in both ways. What I did was just give a bit more security to a team who had conceded in three goals in three away games. At some stage you need to focus on something different for the players to create some confidence.”
Even when Wenger’s defence creaked Arsenal were aided by exceptional individual performances, most notably from Gabriel.
The Brazilian centre-back has been the subject of some criticism since his arrival in January 2015 but was a colossal force in Arsenal’s rearguard.
Wenger told Standard Sport: “Gabriel has played some positive games as a right-back. I felt that he was covered by somebody who had good pace, I felt he could cover for Chamberlain on Sane’s ball through.
“Sane goes a lot in behind and Gabriel has the pace to cover in behind, to tackle, and he did that very well. Especially in the second half.
“He saved three or four goals.”