Bristol Manor Farm recovered from two goals down to win on penalties at the Mettal Stadium.
Town went in front on 36 minutes when Jordan Alves latched on to Harry Hoath’s pass and rolled the ball home.
Toby Fisher ensured the Kingfishers led at the break, palming over from Evander Grubb and Jayden Nielsen.
Alves extended Thatcham’s lead on 49 minutes from a penalty after Mo Ceesay was fouled, and was later denied his hat-trick by the woodwork, then a flying save by Sethan Locke.
But Manor Farm’s second half substitutions changed the game as Mason Winter slotted home from Grubb’s lay-off, then Owen Brain swept home following a short corner routine.
Both teams had chances to win as, despite the heat, the game became stretched and frantic.
But in the shoot-out Locke saved from Alves, Callum Willmoth and Christian Johnson as Manor Farm triumphed 3-1. Owen Clark converted the Kingfisher's one successful spot-kick.
TEAM : Fisher, Heholt, Rohart-Brown, Willmoth, Coates, Blackwood, Alves, Jones, Johnson, Hoath, Ceesay.
SUBS ON : Clark
SUBS UNUSED : Duodu, Wallace, Bangura