The Pilgrims trailed 2-0 to Blyth Spartans at Cochrane Park inside five minutes – before eventually losing 4-1.
Rhys Smaller scored United's consolation goal in the 85th minute.
Boston: Zach Marsh, Rueben Fogg, Oliver Houlston, Dexter Tomlinson, Charlie Brooks, Kirils Snikeris, Toby Cotton, Jake Thompson (Denis Matei 60), Will Pettitt, Oliver Callaby (Daniel Bridges 80), Ryan Makings (Rhys Smaller 55). Sub (not used): Austin Barker (gk).
Referee: Ronnie Faichen.