Lee Clark admitted Wigan Athletic were full value for their 4-0 victory at the DW Stadium on a "horrible day" for his Birmingham side.
Blues never got into their stride as Wigan recorded a second successive win - and clean sheet - on the bounce without much fuss.
Callum McManaman was again the pick of the Latics players with two first-half goals as the home side led 3-0 at the break. Andrew Taylor and substitute Martyn Waghorn grabbed the others for Wigan.
"Everything's that's been good about us has been flipped on its head today," Clark said. "The hard-working and powerful team that everyone has been talking about - even Uwe (Rosler) in his pre-match comments was very complimentary - wasn't there.
"The scoreline doesn't flatter Wigan at all, that was the difference between the two teams. It was like chalk and cheese.
"We didn't stick to what we've been doing really well.
"Our decision-making was poor, our defending was poor, our movement and options for the man on the ball was non-existent, and our passes to the strikers weren't there.
"All in all it was a really horrible day for us."
Clark now has a fortnight to mull over what went wrong, and the Birmingham boss admitted his players will pay the penalty over the forthcoming international break.
"I'd like the next game to come as quickly as possible, but it means we have got two solid weeks where we can get the players in," he added.
"Certainly the schedule that was planned for the players has to change, because we have to get back on the training ground and work.
"The players have to know that a performance like that is unacceptable, and they won't get the luxury of having as many days off as they were going to.
"I didn't see that coming - that's for sure.
"We were so dull in possession of the ball. We needed five or six touches to decide what we were going to do, when you should know what you're going to do before it's even arrived.
"The two substitutions at half-time lifted us, we started playing more like we can, but they get a poor fourth goal which caps a frustrating day."
For his part, Uwe Rosler was in buoyant mood after seeing his Wigan side back up last weekend's 1-0 victory over Blackpool - which hugely flattered the Seasiders - with a second win of the season.
"It was a perfect follow-up from the Blackpool game - a mirror image," he said.
"The one big difference was this time we made the goalkeeper work, we were clinical.
"It was collectively a very strong performance, and it's nice to sign off for a two-week break with back-to-back wins.
"We know we can score goals and we showed that today. "
It was the perfect way to end a week dominated by the breakdown of James McArthur's proposed move to Leicester - something Rosler had been worried might have an effect on his side.
"I was a little concerned - even I wasn't as prepared as I would normally be," he added.
"There was a lot going on, but that is why I have quality coaches around me, and they did a lot of the preparation work so I could do what I had to do.
"The players looked focused on Friday and in the warm-up. They weren't affected at all."
Before the game, Wigan paraded Tours striker Andy Delort as their latest capture, with a deal for the Frenchman expected to be signed on Monday.