Viv Solomon netted a hat-trick for Blues, whilst his strike partner George O'Neil hit a brace. Liam Truslove was also on target in the game at Wast Hills against the London Lions.
Steve Spooner's side made a great start to the match and were 2-0 up within 12 minutes. They then hit a further four goals without reply, before the visitors scored a late consolation.
Academy coach Steve Spooner was thrilled with his side's display.
"It was one of those performances where it all came together and probably one of our best of the season," he said.
"We were a little bit older than we normally are and that helped against a big and physical Millwall side.
"We made a confident start which came from our ball retention, passing it quickly and good movement.
"We created a lot of chances and were very effective around the 18-yard box. We were 3-0 up at half-time and it could have been more."
Spooner felt that striker Solomon was fully deserving of his hat-trick.
"Viv was on fire all and unplayable," added Spooner. "Every time he got the ball it looked like something would happen - either he'd score himself or create an opportunity for someone else."