City were coming off the back of a 3-1 reversal at Wimbledon last week, while the visitors were still on a high after their 4-0 defeat of Norwich, but Mark McGhee's side have now been learnt how difficult life in Division One can be.
Bryan Hughes (pictured), who scored the Blues' consolation last week, grabbed his second goal of the season after 22 minutes by heading in a cross from Australian international Stan Lazaridis.
The young Welshman then added to his tally just five minutes later when he got on the end of a Nicky Eaden cross and beat Tony Warner with his header.
Then, before The Lions could draw breath, the game was put beyond their reach with a third after 28 minutes. Geoff Horsfield claimed his first of the season when he latched on to a Tommy Mooney through ball before finishing cooly.
Millwall attempted to come back into the game, but Birmingham kept coming forward and just before half time they scored a fourth final goal through Eaden. This time man-of-the-match Hughes turned provider for the former Barnsley-man who finished well.
After the game Birmingham manager Trevor Francis paid tribute to Hughes.
"Bryan Hughes was outstanding," he said. "He is a talented player and has not, so far, achieved what he is capable of producing. But with three goals in the opening two games he has made a good start."
"He prefers to play in the middle and if he can maintain this kind of form he will be accommodated in the team.
"A major factor is his ability to time his runs into the penalty area as he demonstrated with his two goals. He deserved a hat-trick and very nearly got his third goal."
Click below for Match summary, including a full match report:
Birmingham City 4 Millwall 0
