A 30-yard strike from 17-year-old Josh Carson on 52 minutes took former England goalkeeper David James by surprise and nestled in the bottom corner to give Ipswich the points.
They had been reduced to 10 men after 28 minutes when midfielder Lee Martin was red-carded for a lunging challenge on Kalifa Cisse, who had appeared fortunate to get away with a similar tackle a couple of minutes earlier.
Millen said: "I'm frustrated and angry that we didn't do better playing against 10 men for so long. Our final ball into the box was poor on too many occasions and when we did get chances we were not clinical enough to take them.
"When it was 11 against 11 I thought we were the better team. But Ipswich got men behind the ball in the second half, which made it difficult to break them down.
"I didn't see anything that I wasn't aware of already and my transfer plans for the summer are already in place. I know the type of players we need and things are already going on behind the scenes."
Source: PA
Source: PA