Birmingham keeper Jack Butland, loaned back after his £3m signing by Stoke last month, was the star of the show before finally being beaten with two minutes left by Yann Kermorgant's headed equaliser.
It seemed the spoils were heading to the hosts, only for Wade Elliott to pounce from six yards deep into injury time to extend the Blues' unbeaten run to five games.
"We eventually got the breakthrough late in the game and were just looking to see it out in a strong way but it hasn't happened and we were disappointed," Powell said.
"We have been in good positions where we needed to see it out and it is something we are going to have to learn from."
While Blues boss Lee Clark described his keeper "the bargain of the century", Powell said: "We came across a keeper who was in imperious form.
"He made some really good saves and you could see why he has gone to the
Premier League. Fair play to him because you can see why so many people have been looking at him and why he has been bought by Stoke.
"His decision making and some of his saves were excellent, that kept them in with a chance and sadly so it proved. It's a real shame because the boys performed really well in conditions that were tough."