The Blues stopper saw his reactions pushed to their limit by the West Ham frontman during a 2-2 draw at St Andrew's.
Cole appeared destined to score when he flicked the ball goalwards, with some of his team-mates celebrating before the ball had even hit the net.
However, Foster got the faintest of fingertips to the effort and was able to touch it onto the inside of the post.
"It was probably my best save ever," said the England international, who joined Birmingham from Manchester United over the summer.
"I managed to get literally the tiniest piece of a fingertip to it.
"I thought it had gone in at the time. I had a little look around when I was on the floor and was dead happy and buzzing."
Foster's team-mates obviously expect nothing less than such heroics from their number one, though, as he admits he has received little praise for his fantastic stop from inside the Blues camp.
"The lads haven't been giving me any credit for it," smiled Foster as he prepares to turn his attention to an away date with Stoke on Tuesday night.