Legge was making his debut after signing on loan from Brentford just before the game.
And Allen felt he played a huge part in the Gills beating one of their promotion rivals.
"The team were back to their best and it helps when we can just sign a centre-back in Leon Legge and put him straight into the team because he was out there," said Allen.
"There were parts of the second half when Southend came into it but I expected that, they had a few chances but they couldn't take them and we were unlucky not to double our advantage with Myles Weston hitting the post.
"I thought it was a tremendous performance against a very good side that are on a great run of form."
An early goal from Chris Whelpdale proved to be the difference between the two teams as he latched on to a deep free-kick from Joe Martin in just the second minute to cushion the ball home from close range.
- Sports & Recreation
- Leon Legge
- Myles Weston