The Pilgrims, missing scores of regular players, found themselves on the wrong end of a four-goal scoreline at the New Manor Ground.
United’s woes were compounded when defender Joe Cain limped off through injury with 35 minutes played.
Boston (4-3-3): Jamie Bradley; Jack Foyster, Billy Hodgkiss, Joe Cain (Joe Money 35), Conor Allen; Miles Lynch, Liam Moran, Jack Dykes; Scott Floyd, Karolis Andriulionis (Liam Moxon 55), Bradley Easey. Sub (not used): Steven Dovey.