Wealdstone were knocked out of the FA Trophy after a 2-1 home defeat to Tiverton Town on Saturday.
The visitors took the lead in the 27th minute when Paul Jarvis fired past goalkeeper Luke Woods.
Watford striker Marvin Sordell was handed a debut after joining on work experience and he almost created an equaliser but his cross evaded the home side.
But recalled midfielder David Hicks levelled the tie with a 58th minute corner which flew directly into the net.
Just as the Stones were looking the more likely winners, Phil Walsh popped up to stun them with the winner.
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