Despite trailing 1-0 at half-time, the Pilgrims recovered strongly after the break to record a resounding 4-1 win on the Jakemans Community Stadium 3G pitch.
Goalkeeper Alife Harney was pressed into service as an outfielder late on – and grabbed United's third and fourth goals following earlier efforts from Joe Todd and substitute Stephen Pereira.
Boston: Alfie Harney, Alex Van-Tam, Tyreece Keating (Harry Gunthorpe 70), Toby Foreman, Daniel Fisk, Kye Rook, Aron Ealham, Jaydon Sargent (Jack Dixon 55), Finley McDaid (Stephen Pereira 55), Kiaran Grove (Cody Elgie 55), Joe Todd (Joe Douce 75).
Referee: Alistair Wilson.