Etheridge grabbed Bluebirds substitute Max Watters around his waist to concede an 82nd-minute penalty that was then converted by Will Vaulks to cancel out Jeremie Bela’s first-half goal for the visitors.
His mistake also meant that Blues have now failed to win on any of their last nine trips to the Welsh capital.
Seventeen-year-old midfielder Jordan James missed an excellent chance to settle matters for Birmingham shortly before former Cardiff keeper Neil Etheridge gave away the penalty that saw his old team snatch a share of the spoils.
But Blues boss Lee Bowyer refused to lay the blame for failing to get maximum points at James’ feet.
“The ball was put on a plate for young Jordan by Onel (Hernandez) but I won’t be criticising him because what I saw was a 17-year-old putting himself in that situation and getting himself in the box to get that chance,” Bowyer said.
“He didn’t then blast it over the bar – he was in full control and tried to do the right thing, but the ball just slid wide.
“It was the chance that would have put the game to bed, but we’ve said that so many times this season and I’m disappointed that we didn’t win the game because I felt we were the better side for large periods.
“We also defended really well and didn’t seem troubled in general play until they got the penalty.
“I thought we had controlled the game up to that point and should have taken full advantage of that in the first half. Then, we should have got another goal in the second half from a couple of good chances.
“But we didn’t and a 1-0 lead still leaves things open for them to get a draw and that’s what happened. We didn’t do much wrong, but it was another case of giving two points away.”
A message from the editor:
Thank you for reading. BirminghamWorld is Birmingham’s latest news website, championing everything that is great about our city - reporting on news, lifestyle and sport. We want to start a community among our readers, so please follow us on Facebook,Twitter and Instagram, and keep the conversation going.