Scotland fly-half Duncan Hodge steered Reivers to a 22-16 victory which dented Ponty's Welsh/Scottish League title hopes on a Galashiels gluepot pitch.
The Sardis Road outfit had made a bright start but paid dearly for a spate of mistakes in the dreadful conditions. Hodge capitalised by slotting over six kicks.
Frustratingly for the home support, it was the Reivers who made the bulk of the early errors and they found themselves six points adrift to two Lee Jarvis penalties.
It took the Reivers 23 minutes to mount their first meaningful attack, but they made the most of it. Wing Cammy Murray sparked panic among the Ponty back-markers with a nicely weighted chip.
Reivers earned a penalty in a scoring position, but gambled by going for the line-out near the corner - and they were rewarded for their enterprise.
Centre Marcus di Rollo was blocked just a metre short of the line, the ball was expertly recycled to set up an opening for Hodge.
He was also halted just short, but had the presence of mind to pop it up for giant lock Richard Metcalfe to flop across, giving Hodge a straightforward conversion.
He then added two penalties but Ponty responded strongly by picking up 10 quick points through a Jarvis penalty before he converted a scrambled touchdown by recent signing from rugby league, Allan Hunte, on the stroke of half-time.
Reivers repaired some of the damage in the 55th minute when Hodge slotted his third penalty from 30 metres after handling on the deck, then sealed it with two more strikes.