The new signing from Royston Town rifled home a 25-yarder to hand the Pilgrims a 28th minute lead, although former West Ham United starlet Zavon Hines equalised five minutes later.
In addition to Marriott’s maiden appearance for United, fellow striker Jonny Margetts emerged from the bench in the second half for his own first outing in amber and black.
Boston (4-4-2): George Willis (Dylan Parkin 46), Ben Middleton, Ryan Qualter (Trialist G 46), John McCombe, Jordan Gough (Ashley Jackson 46); Jonathan Wafula (Grant Roberts 46), Brad Abbott (Trialist H 46), Andi Thanoj (Spencer Harris 46), Nathan Arnold (Trialist D 66); Trialist B (Trialist A 46), Adam Marriott (Jonny Margetts 59).
Referee: Declan Bourne.
Attendance: 429.