Wenger fielded a defensive trio for the second match running on Sunday and it paid off as the Gunners beat Manchester City 2-1 to book an FA Cup final meeting with Chelsea.
Arsenal had not looked entirely comfortable in their new 3-4-3 formation the previous week, when they ground out a 2-1 win over struggling Middlesbrough, but they were dogged and determined against City, qualities they have so often lacked this season.
It means they have now registered back-to-back wins for the first time since January and rejuvenation would be timely given they host Leicester on Wednesday, before a crunch north London derby against Tottenham four days later.
Koscielny, who played at the centre of the back three at Wembley between Gabriel and the impressive Rob Holding, believes the new system has made Arsenal harder to beat.
“There was a tactical turnaround but we have been working on it for 15 days,” Koscielny said.
“The system suits certain players but it’s also good for the whole team. I think we have also found more confidence in this system with three defenders.
“We are more solid. Commitment and determination also helped us to win because over the whole game we played as a team and fought hard.”
Arsenal are still seven points adrift of fourth in the Premier League and have a tricky run-in which, as well as Spurs, includes matches against Manchester United and Everton.
They do, however, have a game in hand over both United and City, who play each other in the Manchester derby on Thursday, while Koscielny believes his side have turned a corner.
“Before this game we were in quite a dark period, we had lost confidence,” Koscielny said.
“This victory has allowed us to regain confidence and keep calm, even if not everything was perfect.”
Alex Oxlade-Chamberlain is a doubt for the game against Leicester after he took a kick to his ankle at Wembley and later left the stadium on crutches.
Early indications are the injury is not serious but the 23-year-old will undergo tests on Monday to diagnose the extent of the damage.