Tynedale's hopes of following rivals Blaydon with promotion from National League Three (North) were shattered in Kent on Saturday.
The Prudhoe side looked set to make the same step as Blaydon, who had clinched a National League Two spot by beating Tynedale to the title.
But their 17-0 interval lead over League Three (South) runners-up Westcombe Park in their play-off was wiped out in nine second-half minutes as Tynedale lost 36-20.
Tries by Jack Harrison and Phil Belgian - both converted by the latter - and a Belgian penalty had given Tynedale their half-time lead.
Belgian's second penalty put the visitors in front but it was a brief respite as Westcombe won.