The Pilgrims were beaten 3-0 at home by Solihull Moors – who led 1-0 at half-time before adding two further goals after the break.
United will conclude their pre-Christmas schedule with Academy Division North fixtures at home to Chester FC and FC Halifax Town.
Boston (3-5-2): Jake Lovelace; Taylor Redman (Oskar Rajski 73), Owen Sheriff, Taylor Jaine; JJ Ward, Jake Henderson, Han Stevens, Rueben Fogg (Kyle Featherstone 78), Josh Doran (Lucas Stubbs 78); Krisztian Gagyi (Patrik Bad 70), Flynn Slater. Sub (not used): Cameron Fox (gk).
Referee: Alistair Wilson.