The match was finely-poised at 1-1 in the second half, courtesy of Squire’s strike, but three quickfire goals took the contest away from United, who were led by assistant manager Martyn Bunce for the day.
Harriers’ goals were scored by Adam Gwilliam, James Odagi, Kennedy Digie and Jordan Harrison.
Boston (4-4-2): Jamie Bradley; Daniel Worthington (Harry Bunce 60), Josh Spencer, Joe Cain, Corey Newman; Leon Squire, Jacob Pease (Miles Lynch 60), Ollie Price, Aaron Eyett; Liam Moran, Steven Dovey (Karolis Andriulionis 60).