It took just 6 minutes for Town to open the scoring as Christian Johnson prodded Andy Matthews’s header from Callum Willmoth’s free-kick home at the far post.
Barely ten minutes later it was two, as Shamar Moore rifled home into the roof of the net from a tight angle, following good approach play from Mo Ceesay.
Thatcham's third arrived on 50 minutes, with Willmoth, Moore and Kyle Daniel-Spray involved in the build-up. Jamie Davies was found on the edge of the box and the Maidenhead loanee fired emphatically into the top left corner.
Athletic keeper Andrew Sowden had earlier made a flying save to keep out a Daniel-Spray free-kick, then got a vital hand to the ball when Moore pounced on a loose back-pass. Near the end Ceesay headed over from Daniel-Spray's centre.
Although Helston created relatively few chances, the Town defence defended a number of corners well. James Sharlott was called into action to push Liam Eddy's shot around the post, and then tip Craig Duff-Dick’s header over the bar, and kept his second successive clean sheet.
Team : James Sharlott, Ben Portbury, Kyle Daniel-Spray, Callum Willmoth, Oli Bourne, Andy Matthews, Shamar Moore, Jadyn Dundas, Christian Johnson, Mo Ceesay, Jamie Davies
Subs on : Shyam Taank, Dan Smith, Jenson Mansel, Harvey Flippance.
Sub unused : Kaser Chowdhary