Having harboured play-off aspirations at the start of 2017, a run of just two league wins in nine outings has sent the Ducks spiralling down to 15th in Division One Central.
They made on change for the visit of Ashford, bringing in Gavin Hinds-Cadette, and with a strong wind behind them, United made their customary bright start.
Bruno Bito and Lea Coulter just failed to reach Jake Bewley’s overlapping cross before, in the 11th minute, the home side struck first blood.
Jack Wood won possession on halfway and played a fine ball into the path of Bewley, whose low cross was this time perfectly placed for Coulter to tap in from six yards.
The lead was to last just two minutes, as the away side’s top scorer Mark Bitmead equalised. After getting free down the right, he shot from 15 yards to see Jack Sillitoe parry the ball, only for the rebound to fall back to the striker and he dispatched his effort to level.
Brito was in the thick of the action twice around the half-hour mark when volleying wide of goal before a loose pass set up an Ashford counter-attack that was only stopped by a last-ditch block.
Dan Fleming was denied by Sillitoe for the visitors before the Ducks squandered a golden chance to level on the cusp of half-time as skipper Wood struck the woodwork.
Starting the second-half with the conditions in their favour, Ashford soon put the home defence under pressure. A hurried clearance by Bewley saw the ball fall to Tommy Brunton, but he fired wide.
Bitmead was then denied by Sillitoe, followed shortly by Max Hebert shooting wide.
By now, the Ducks were finding it hard to retain possession for any sustained period and with the visitors dictating play, only one team looked like winning it.
With 10 minutes left, Brunton found Mummeryx whose shot was saved at his near post by Sillitoe. Skipper Russell Canderton saw his free header from the subsequent corner saved but rebound back to him and this time he made no mistake to give his side the lead.
It was to be the decisive moment of the match and condemned United to a 10th home defeat of the league season.
Next up is the visit of Egham Town this Saturday.