
The best chance in the first 40 minutes came in the opening minute as Maciej Wieczorek saved low to his left to keep the visitors at bay.
But as half-time approached, Knaphill opened the scoring when Lynford Sackey won possession and fed Olly Woolgar who finished emphatically.
Town crumbled as the interval approached, with Woolgar and then Ben Mitchell firing in goals two and three.
Thatcham pressed more after the break and pulled one back on the hour. Ali Thorp was set free down the right channel and rolled the ball past the keeper and into the corner for a debut goal.
That goal lifted Thatcham who played with more belief, and Callum Willmoth struck the crossbar from a free-kick.
But the visitors countered well to score through Sackey to put the result beyond doubt.
Substitute Junior Da Cruz got through the back line and saw his shot deflected on to the post, with no one able to put the loose ball over the line. But a second goal did arrive on 88 minutes as Callum Winchcombe forced home his fourth goal of the season.
However the Knappers carved Thatcham opened twice more during time added on, with Elijah Hopwood skipping down the left to tee up Rami Halloufi, then Maurice Black netting a similarly easy chance in front of goal.
TEAM : Wiezcorek, Edwards, Winchcombe, Willmoth, Voller, Boylan, Polding, Denton, Thorp, Smith, Denner.
SUBS ON : Clark, J Da Cruz, Barker.
ATTENDANCE : 119