The Pilgrims were beaten 1-0 by Solihull Moors at Studley Sports Centre.
The result leaves United with four points from their opening three fixtures of the Academy Division North campaign.
Boston (4-3-3): Cameron Fox; Bailey Dilley, Sam Harris (Jake Higginbottom 70), Owen Sheriff, Taylor Jaine; Mackenzie Burdass (Patrik Bad 65), Han Stevens, Jake Henderson; Rueben Fogg, Flynn Slater, JJ Ward (Josh Doran 78). Subs (not used): Kyle Featherstone, Kelton Robinson.
Referee: Dave Badger.