Both teams had players sent off, with James Mallender red-carded for the Pilgrims, who got themselves on the scoresheet through Jamie Gaukroger, Jack Bastow and Lewis Bontoft.
Guiseley striker Raf Ferreira scored seven times as Guiseley wrapped up an 11-3 win at The Jakemans Stadium.
Boston (3-5-2): Jake Frestle; James Mallender, Harry Cranfield, Arron Bailey (Lewis Bontoft 46); Jamie Gaukroger, Henry Beedham (Xander Crashley 46), Brogan Horniman, Joe Hardstaff, Ben Johnson; Tom Wilkinson, Jack Bastow.
Referee: Ian Ruddock.