Early goals from Dwayne Wiley and Liam Waldock set the tone - with United punished for some haphazard defending.
Lewis Salmon added a second half brace - the second of which arrived in stoppage time - as the Reds romped to a resounding home win.
The Pilgrims, with Michael Bostwick and Martin Woods back in the starting XI, fell behind in the eighth minute when WILEY was afforded the freedom of the penalty area to sweep home Adam Lund's long throw.
The Reds doubled their lead 14 minutes later when Brad Nicholson's square ball was cut out and WALDOCK was able to roll home Alfreton's second goal.
Ex-Pilgrim George Willis had a number of long-range efforts to field either side of half-time, but was not seriously troubled, although Jimmy Knowles should have reduced the arrears when he crashed into the side-netting in the 66th minute.
Alfreton sealed the deal two minutes later when SALMON steered home from close-range, despite the close attentions of Nicholson, as the Reds moved three goals in front.
The hosts completed United's miserable afternoon in stoppage time when George Cantrill rattled the post, with SALMON sweeping home his second into an empty net.
Alfreton (4-2-3-1): George Willis; Josh Clackstone, Kennedy Digie, Shaun Brisley, Dwayne Wiley; George Cantrill, Adam Lund; Lewis Salmon, Liam Waldock, Billy Fewster (Nathan Newall 87); Jake Day. Subs (not used): James Oliver, Anthony Dwyer, Will Pollard, Jake Askew (gk).
Boston (4-1-2-1-2): Cameron Gregory; Zak Mills, Tom Edge, Michael Bostwick (Dylan Hill 73), Brad Nicholson; Martin Woods; Jordan Richards, Sam McLintock; Keaton Ward (Michael Gyasi 66); Finley Throndike, Jimmy Knowles. Subs (not used): Keziah Martin, Sam Essien, Tyler Knowles.
Referee: Shaun Taylor.
Attendance: 753.
PIC: Chris Bray.