United led through Scott Garner on 50 minutes, but were forced into a penalty shootout when Haydn Hollis equalised with 15 minutes to play.

Ex-Chesterfield duo Jordan Burrow and Connor Dimaio subsequently failed to score from 12 yards, as the Spireites converted four successful spot-kicks.

It left the Pilgrims to solely concentrate on the remainder of their National League North campaign, with Chesterfield booking a fifth round trip to Aldershot Town in the process.

An early Andi Thanoj free-kick was beaten aside by Chesterfield’s debutant keeper Dylan Wharton, while Ross Fitzsimons made a fine double save to thwart Joe Rowley.

Rowley was subsequently freed down the right by Liam Mandeville, but crashed an effort into the side-netting.

Jay Rollins was denied by a Will Evans goalline clearance after Wharton had failed to deal with a cross from Leesley.

United took the lead five minutes after half-time when Leesley’s corner was powered home by the head of GARNER, for his fourth goal of the season, with Wharton misjudging the flight in the swirling wind.

Hollis presented Dimaio with a glorious chance to double United’s lead, but the Boston midfielder inexplicably crashed his clear sight of goal over the North Stand.

Fitzsimons was almost the unlikeliest goalscorer when his downfield clearance caught the wind, bounced over Wharton and came back off the crossbar.

Leesley produced a brilliant block to deny Josef Yarney but the resulting Jak McCourt corner brought Chesterfield’s equaliser – with HOLLIS glancing home a fine header.

Laurence Maguire, Rowley, McCourt and substitute Tom Whelan fired home Chesterfield penalties – but Wharton’s save from Burrow and Dimaio firing wide proved costly for United, although Paul Green did confidently convert his spot-kick to briefly reduce the arrears to 2-1.

Boston (3-5-2): Ross Fitzsimons; Matt Tootle, Luke Shiels, Scott Garner; Jay Rollins (Terry Hawkridge 90), Paul Green, Andi Thanoj, Connor Dimaio, Joe Leesley (Scott Duxbury 86); Jordan Burrow, Jordan Thewlis (Jake Wright 76). Subs (not used): Tyrell Warren, Mitch Rose, Fraser Preston, Peter Crook (gk).

Chesterfield (3-5-2): Dylan Wharton; Will Evans, Haydn Hollis, Laurence Maguire; Josef Yarney, Joe Rowley, Curtis Weston, Martin Smith (Jak McCourt 58), George Carline; Marcus Dinanga (Akwasi Asante 46), Liam Mandeville (Tom Whelan 72). Subs (not used): Jack Clarke, Regan Hutchinson.

Referee: David Richardson.

Attendance: Behind-Closed-Doors.

Photography: Russell Dossett.