Andrew Oluwabori scored inside the first minute as FC Halifax Town left the Jakemans Community Stadium with all three points on Saturday afternoon.
Oluwabori netted on exactly 60 seconds as the Shaymen got off to the best possible on their first visit to Boston for seven years.
Jacob Hazel was denied by a brilliant Will Smith goalline clearance after the break, while debutant Finley Welch rattled the post, but Halifax held on.
United boss Ian Culverhouse had opted to make five changes ahead of kick-off, with on-loan Norwich City youngster Welch one of those to come into the starting XI.
The Pilgrims were chasing from the outset though with OLUWABORI closing down a Kieran Coates clearance, rounding his opponent and angling an effort into the far corner beyond the reach of Aidan Stone.
Michael Bostwick bulleted a header wide in response from a Cameron Green free-kick, but first half chances were at a premium.
United stepped up a gear after the break, with Sam Osborne firing over from long-range, while Smith excelled seven minutes into the half to deny Hazel on the line, with keeper Sam Johnson wandering.
Bostwick saw another header drop narrowly wide from a Keaton Ward corner.
Welch cracked an effort against the post with 10 minutes to play, while Halifax ended with 10 men with Adan George handed the second of two soft yellow cards on the stroke of 90 minutes.
Boston (4-2-3-1): Aidan Stone; Kieran Coates (Jai Rowe 62), Michael Bostwick, Zak Mills, Cameron Green; Jordan Richards, Dylan Hill; Sam Osborne (Pemi Aderoju 74), Keaton Ward, Finley Welch (Frankie Maguire 82); Jacob Hazel. Subs (not used): Tom Leak, Adam Marriott, Jude Frostick, Ellis Craven (gk).
Halifax (4-3-3): Sam Johnson; Adam Senior, Jo Cummings, Will Smith, Ryan Galvin; Jamie Cooke (Florent Hoti 72), Scott High (Owen Bray 63), Jack Evans; Adan George, Billy Waters, Andrew Oluwabori (Adam Alimi-Adetoro 82). Subs (not used): Harvey Sutcliffe, Jack Jenkins, Tom Pugh, Nathaniel Ford (gk).
Referee: Paul Cooper.
Attendance: 1,720 (188 visitors).
PIC: Tim Hoff.
