Thatcham were dominant in the opening stages with Harry Hoath narrowly off target, then having a shot saved by Josh Addison. Sam Tanner then thumped the underside of the crossbar from 12 yards following a flowing move before the visitors attacked down the right and Sam Murray headed over.
However the Kingfishers did open the scoring on 34 minutes when David Nyarko was allowed to advance deep into the Guernsey area and clipped home a near post finish.
Then a minute later Harry Hoath added a second, slotting home from Tinashe Gwavava’s low pass.
Guernsey pulled themselves back in to the contest on 44 minutes when a cross bounced across the penalty area and Keene Domaille blasted home.
On the stroke of half-time Nyarko and Hoath almost extended Town’s lead but both saw close range shots blocked by Addison and his defence.
In the second half Thatcham continued to dominate play and added a third when Mo Ceesay headed home Callum Willmoth’s free-kick on 56 minutes.
Nathan Jones sidefooted wide, and Levi Heholt broke forward and fired a 40-yarder towards goal which Addison kept out.
Substitute Jordan Alves caused problems down the right wing, and from one of his surging runs he pulled the ball back for Christian Johnson to add a late fourth.
The visitors had a late chance when Toby Fisher raced out of his area to head clear, but Matt Loaring’s shot from distance sailed over the bar.
Team : Fisher, Gwavava, Daniel-Spray, Willmoth, Heholt, Angell, Tanner, Jones, Nyarko, Hoath, Ceesay
Subs on : Alves, Johnson, Clark. Subs unused : Smith