Leyton Orient's second away win of the season was built on the foundation of some in depth second-half defending.
Their packed defence successfully protected an early goal from Chris Tate and the result brought up an unwanted seventh successive league and cup defeat for Boston.
What proved the decisive moment came on five minutes when the visitors gained the upperhand.
Home defender Mark Greaves failed to clear a cross by Matthew Lockwood and Tate fired home from 18 yards via a deflection off Matt Hocking.
That goal gave Orient a confidence boost and Tate again went close with a low drive that was well held by Paul Bastock.
Boston struggled to find any real spark against a well-drilled Orient back line with only off target efforts by Simon Weatherstone and Greaves threatening Scott Barrett's goal.
The Pilgrims were guilty of squandering possession in several instances and repeatedly fell into Orient's offside trap.
The closest they came to an equaliser was in the 35th minute when a rising drive from Weatherstone flashed inches too high.
Then in the 43rd minute a rare show of skill and determination down the right saw Peter Costello cut in and fire a drive against the bar.
Boston threw on substitutes Richard Logan and Tom Bennett and began the second half full of fire with Costello having a cross shot blocked and then referee Mick Warren waving away loud penalty appeals after Ezomo Iriekpen appeared to handle the ball.
As Boston pressed again Logan saw a shot saved by Barrett and Costello fired wide as Orient withstood more sustained home pressure.
There was no let up in Boston's assaults and in the 75th minute Barrett produced a spectacular save to keep out Ben Chapman's long-range piledriver.
As the game entered its final quarter Costello again joined the Boston attack and forced another fine stop from Barrett.
Apart from one off target shot by Lockwood, Orient's second-half forays were non-existent as they relied on solid in-depth defending.
And towards the end Barrett again kept his side ahead by frustrating Weatherstone and Costello as Boston were repelled once more