The Arsenal pair’s mix-up in that game allowed Obafemi Martins to score a last-minute winner for Birmingham City.
But Wenger says the huge strides Koscielny and Szczesny have made since then prove the importance of not rushing to conclusions.
Since that incident in the League Cup final, Koscielny and Szczesny are two of the most improved playersArsène Wenger
“Koscielny is one of the best in Premier League, without any hesitation,” the manager said. “He has combination of qualities. Good reading of game, good anticipation, great commitment, great speed and [he is] quick on the turn.
“He is good on ball but he has improved a lot in that he now has better control of himself. He is more serene and calm, one of the very best for sure.
“He had a tough spell after [the League Cup final] and last year I took him out of the team for a while. That’s where I give him great credit because he came back in convincing way and took being left out in a positive way.
“I was thinking about that situation this week. Since that incident in the League Cup final, Koscielny and Szczesny are two of the most improved players. You questioned them but this shows you have to be open-minded.”
Wenger insists he never considered signing replacements for either player - and he has been fully vindicated.
“I was questioned on that, especially with Wojciech - there was a pressure there,” he said. “But he is still very young for a keeper at that level and this season I think he has proven it was the right decision.”Copyright 2016 The Arsenal Football Club plc. Permission to use quotations from this article is granted subject to appropriate credit being given to www.arsenal.com as the source