The Pilgrims led Spennymoor Town courtesy of Dominic Knowles' eighth minute goal and were only denied a second for Martyn Woolford when Knowles was penalised for offside on the line.
The Moors responded within seconds through James Roberts and secured all three points through Shane Henry's long-ranger in the 66th minute.
United, with Alex Penny and Jonathan Wafula coming into the starting XI in the places of the injured Simon Ainge and suspended Tom Platt, opened brightly.
Penny saw a shot deflected wide after Wafula had nodded on Martyn Woolford’s deep corner and then Luke Shiels headed over the bar following Andi Thanoj’s corner delivery.
United took an eighth minute lead when Jordan Thewlis fizzed a cross into the box from the right and KNOWLES stabbed the ball home from close-range.
The Pilgrims thought they had doubled their lead when Woolford blasted home from another Thewlis cross, but assistant referee James Cann deemed that the ball had struck Knowles in an offside position.
Spennymoor took full advantage and levelled within a minute when ROBERTS showed good composure to beat Peter Crook from 18 yards.
United went close seven minutes after half-time when Knowles’ firm header was repelled by Jake Hibbs following Thewlis’ deep cross from the right.
The Moors took the lead for the first time midway through the half when HENRY shrugged off the attentions of Wafula to drive forward and arrow a left-footer into the top corner of Crook’s net.
United thought redemption had arrived in the 77th minute when Penny blasted goalwards on the end of Woolford’s free-kick, but his effort was kept out by a clutch of bodies.
Spennymoor (4-2-3-1): Matt Gould; Jake Hibbs, James Curtis, Nathan Buddle, Chris Mason; Jamie Chandler, Shane Henry; James Roberts (Adam Boyes 88), Rob Ramshaw, Mark Anderson (Ben McKenna 66); Glen Taylor. Subs (not used): Stephen Brogan, Gavin Cogdon, Dan Ward.
Boston (4-3-3): Peter Crook; Demeaco Duhaney, Luke Shiels, Alex Penny, Alex Whittle; Brad Abbott, Andi Thanoj, Jonathan Wafula (Jay Rollins 80); Jordan Thewlis, Dominic Knowles (Shaun Tuton 86), Martyn Woolford (Jake Wright 80). Subs (not used): Ashley Jackson, George Willis (gk).
Referee: Adam Herczeg.
Attendance: 930.