The Pilgrims accounted for Blyth Spartans at the Jakemans Community Stadium.
Blyth were reduced to 10 men before half-time - but United were unable to add to the scoreline after the break despite creating a hatful of presentable chances.
Boston (3-4-1-2): Oliver Ford; Taylor Jaine, Owen Sheriff, Ben Robson; Krisztian Gagyi, Mackenzie Burdass, Finlay Armond, Zane Millar; Han Stevens, Ben Johnson; Sam Harris. Subs (used): Logan Tate, Joe Melson, Jack Waddington, Charlie Wilkinson (gk).
Referee: Istvan Mod.