Szczesny, elevated to Arsenal's first choice at just 20 years of age following injury to his fellow Pole Lukasz Fabianski and Manuel Almunia's loss of form, was at the heart of the defensive mix-up that led to Obafemi Martins scoring Birmingham's winner two minutes from time.
Foster, who used an I-Pod to remind himself of how Tottenham Hotspur players took penalties before helping Manchester United win the League Cup two years ago in a penalty shootout, was named man of the match.
"He was absolutely brilliant," his manager Alex McLeish told reporters. "He showed how good he is even saving balls with his face.
"He has been awesome, he was solid, he's a very good goalkeeper.
"His kicking tactically was excellent today - we worked on some things, and he kicked very accurately which was part of the plan," said the Scot, adding that it was probably the greatest achievement of his career.
"Relatively speaking it is," he said. "For me to come to England and for a small club like Birmingham to beat mighty Arsenal, well no-one gave us a prayer," he said.
Foster made three outstanding saves from Samir Nasri and stopped what looked like certain goals from Andrei Arshavin and Nicklas Bendtner but he had no chance of stopping Robin van Persie's excellent equaliser.
"My view is that there was a lack of communication and determination because when the ball is in no-man's land, someone has to take responsibility and go for it really," Wenger said.
"What was amazing is that no-one from Birmingham was going for it either."
