Nick Lovelace's side found the going tough at the Valley Stadium, with the home side running out 5-0 victors over the Pilgrims.
United's preparations were not helped with midfielder Charles Doble sustaining an injury in the warm-up.
Boston: Oscar Broom, Alex Van-Tam, Jack Clayton (Finley McDaid 72, Jake Leggate 75), Leon Hagger (Lewis Horne 64), Daniel Fisk, Freddie Lound, Harry Gunthorpe, Kye Rook, Matas Gecas, Cody Elgie, Kiaran Grove.
Referee: Dan Tracy.