United led in the seventh minute through Luca Alonzi, after Greg Sloggett had rattled the crossbar, but Town had turned the tables by half-time with goals from Matt Cotton and Zak Munton.
The Pilgrims probed repeatedly after the break, with Manni Norkett's deft header ruled out by a controversial offside flag, but United's trialist striker struck at the death after good work from Michael Kelly and Dylan Hill.
United (first half): Bobby Jones, Ben Grist, Zak Mills, Greg Sloggett, Frankie Maguire, Alex Lankshear, Olly Green, Arjan Raikhy, Luca Alonzi, Jordan Cropper, Trialist A.
United (second half): Rhys Lovett, Michael Kelly, Connor Teale, Rocco Coyle, Dylan Hill, Jacob Scott, Jordan Richards, Liam Waldock, Manni Norkett, Finley Ging, Trialist B.
Referee: Aimee Keir.
Attendance: 572.