The inconsistency of performance is really scary. We played so well last week to this. We went back to the old way of just do what you want.Paul Robinson.
Substitute Amari Miller scored Blues' goal in the 63rd minute, but the overall performance was one that left Paul Robinson frustrated.
Blues have a private friendly as part of their preparations before making the Third Round trip to Sunderland on 12 December.
"It was very frustrating," said Robinson, Blues' Lead Professional Development Coach.
"The inconsistency of performance is really scary. We played so well last week to this. We went back to the old way of just do what you want.
"The players have to realise they are in a ruthless sport, where you can't just expect to turn up and win games.
"It just doesn't happen. You have to be at it every week. You have got to be listening to all the information given to you, take it all on board and do the right things.
"At the moment we're not getting that. Yes, they are a young group, but this is football."
Blues lost Oumar Traore to injury in the 16th minute.
"Oumar, it was his hamstring," said Robinson. "Don't know the full extent of it yet.
"That throws the team, with all the preparation you have gone. You have to make a change quickly.
"But I thought Amari was very bright and alert to things when he came on, he did his role well to what we asked of him.
"That's all he can do. He is one of those who has been a real positive as he's always wanting to learn, he's always wanting to be better.
"When he came on he added a little extra dimension to us with his pace and directness."
Robinson continued: "We scored a really good goal. We could have got back into it after that.
"I would say the last 20 minutes were a lot, lot better.
"But, again, it's not what we are used to seeing from them. It was a below par performance."
Blues: Rouse, Oakley, Djurovic, Chang, Browne, Craig, Williams, Walker, Zohore, Traore (Miller 16), Hurst.
Subs not used: Mayo, Dugmore, Finnegan, Fogarty.