Marc Newsham netted his 29th goal of the season... but it wasn’t enough as the Pilgrims went down 2-1 to promotion-chasing FC Halifax Town.
The leading scorer’s spot kick saw him equal his best tally for United - which last came in the 2009-10 UniBond Premier promotion-winning season.
But the day belonged to the Shaymen, who sit comfortably in the Blue Square Bet North play-off zone.
After a sloppy start to the match, the Pilgrims finally got a grip on the game, carving out the opening two chances.
Arguably, the last person you’d want the ball to land to 12 yards from goal is a centre back.
But that was the case as Phil Watt was granted a free volley following Ian Ross’ free kick, his wild lash seeing the ball sliced well off target.
And when Ben Fairclough created a shooting opportunity on the edge of the penalty area his effort was too weak to worry Matt Glennon.
The Shaymen should have taken the lead when Lee Gregory was put through on goal, but his lob - after United keeper Dan Haystead rushed off his line - was struck too heavily and the opportunity went begging.
Back came Boston, with right back Conor Marshall finding space to unleash a low drive from distance.
However, his effort whizzed wide of Glennon’s near post.
Failing to convert those chances came back to haunt United in the 41st minute, when Chris Worsley volleyed Halifax in front.
Ryan Toulson’s inviting cross was met by the midfielder - ghosting in between Watt and Marshall - who had time to pick his spot and side-foot beyond Haystead.
But there was more bite to United after the break, and the hosts pulled level thanks to Marc Newsham’s penalty on 54 minutes.
He scored his 29th of the season from 12 yards out, sending Glennon the wrong way after Gary Silk was needlessly chopped down by James Knowles.
In the ascendancy, Newsham saw two efforts from close range fail to find the net, while Ross’ free kick was beaten away by Glennon.
But then a moment of class put Halifax back in front.
Alex Titchiner weaved in between Silk and Stainfield before beating Haystead with a low drive in the 67th minute.
A momen t of neat control in the box from Ross almost pulled the Pilgrims level again, but his effort was well-saved by Glennon at his near post.
At the other end, Shaymen sub Danny glover almost made an immediate impact, but his close-range effort was defelected over.
UNITED: Haystead, Marshall, Silk, Fairclough (Sanders 80), Watt, Stainfield, Ross, Milnes, Weir-Daley, Newsham, Mills (Fioster 66); Subs (not used): Ward, Field, Lister.
HALIFAX: Glennon, Toulson, McManus, Bolton, Knowles, Lowe, Worsley (Glover 82), Williams, Titchiner (Johnson 85), Gregory, Worthington; Subs: St Juste, Needham, Senior.
Ref: Lee Betts.