The Pilgrims were excellent during a tight and well-contested first half at the International Stadium but imploded inside an eight-minute period after the break.
Nicky Deverdics, JJ O'Donnell and Dominic Tear struck on 53, 57 and 61 minutes respectively to send Craig Elliott's side home empty-handed.
United went within a whisker of taking a first minute lead when Andi Thanoj curled a 20-yard free-kick into the side-netting.
Thanoj then provided the corner delivery which Tom Platt nodded narrowly wide of the far post.
United keeper Peter Crook had to be alert to keep out Deverdics’ driven free-kick before the break, with Tear firing the follow-up into the side-netting.
The Pilgrims had a further opportunity before the break, but skipper Luke Shiels miscued in front of goal following Thanoj’s free-kick delivery.
Gateshead missed a gilt-edged chance on the stroke of half-time when Greg Olley stabbed wide of the far post following enterprising play from Tear down the right.
Tear supplied the ammunition for Gateshead’s breakthrough eight minutes after half-time when he laid the ball off for DEVERDICS to arrow an effort low into the corner of Crook’s net.
Olley then drilled in a cross from the left which was deftly flicked home by O’DONNELL at the near post four minutes later.
Four minutes further on, Gateshead killed the contest when TEAR rounded off a fine team move with the Heed’s third goal in the blink of an eye.
Lewis Gibbens and George Green were both thrown on as United went 3-5-2 and Dominic Knowles soon found himself through one-on-one, only to be denied by home keeper Brad James.
Jordan Preston’s deflected effort rattled a post for Gateshead late on, but the hosts had long since secured all three points.
Gateshead (4-3-3): Brad James; Alex Nicholson, Toby Lees, Michael Nelson, Scott Barrow; Liam Agnew, Nicky Deverdics, JJ O'Donnell (Jordan Preston 80); Dominic Tear (Elliott Forbes 88), Josh Kayode (Paul Blackett 90), Greg Olley. Subs (not used): Danny Greenfield, Sam Guthrie (gk).
Boston (4-3-3): Peter Crook; Karl Byrne (Lewis Gibbens 64), Luke Shiels, Simon Ainge, Alex Whittle; Brad Abbott (George Green 64), Andi Thanoj (Jordan Adebayo-Smith 77), Tom Platt; Jay Rollins, Dominic Knowles, Jordan Thewlis. Subs (not used): Nicky Walker, George Willis (gk).
Referee: Richard Holmes.
Attendance: 1,134 (85 visitors).