New signing Cassidy struck ten minutes from time to take all three points back to Berkshire for the Stripes.
The two sides were given a rapturous reception by the home crowd and it was the Hatters who almost broke the deadlock early on - Jordan Keane testing the visitors keeper.
Chances were at a premium with both sides threatening from distance but it remained goalless at the break.
Whatever Alan Devonshire said to his team during the interval worked as his side looked much more sprightly in the early stages of the second-half.
Just before the hour mark, Jake Kirby rounded Taye Ashby-Hammond but was thwarted by a goal line clearance.
The only goal of the game came in the latter stages when Jake Cassidy capped his debut with a looping header to send the 64 travelling fans home with a smile.
Jim Gannon introduced Nyal Bell and Ben Jackson but the Hatters couldn't find a way through the stubborn Maidenhead defence.