Bideford coach Simon Morrell has seen his side improve in recent weeks, but probably did not expect them to turn over the third-in-the-table Saints.
What made it all the more remarkable was that the team was seriously depleted by the guest list for player Peter Bowes wedding.
Bideford had not led in any game this season until Harry Jones scored the first of his two tries.
Further tries from Jones and Nick Evans, plus two penalties and a conversion from Pat Sanders, kept Bideford ahead, just.
Bideford are still bottom, but have trimmed the gap between them and safety to eight points.
“The next four games are going to be crucial,” said Morrell.
“We believe we can better the teams around us in the back leg of the season but need to close the gap before we enter that phase.
“Three more wins before Christmas will certainly go a long way towards achieving this.
“To do that we need to build on Saturday’s performance, which was by no means our best.
“We have plenty left in the tank and we certainly intend to play ourselves out of this dark hole.”