Alchester held on to defeat morning leaders Bletchley 17-15 at their Fritwell ground in Southern Counties North.
As a result of their fourth victory in five matches, Alchester overtook Wallingford to go ten points clear of the drop zone.
Fly half Tom Miles kicked Alchester ahead with a penalty, but Bletchley exploited mistakes by the hosts to score two tries for a 10-3 lead at the break.
Alchester had two tries disallowed when the referee was unsure over the grounding, but openside flanker Matt Flegg forced his way over for Miles to convert.
Hooker James Hay scampered over for Alchester’s second try, Miles converting for 17-10.
Bletchley managed a third try, but Alchester closed out a memorable victory.