The Sky Blues were rarely in the contest at Portman Road and had only Stephen Hughes' superb second-half free-kick to show for a below-par performance.
Dowie said afterwards: "One team could defend and the other couldn't. We gave a very poor defensive display.
"The first goal we conceded was a litany of errors. I put it down as a blip. I hope it's only a blip because I cannot put up with defending like that.
"We will all have to work hard on the training ground during the week. We allowed (Jon) Walters and (Alan) Lee to dominate us in the air."