The Pilgrims' main youth team were beaten 2-1 by league leaders Farsley Celtic at West Riding FA.
United's goal was scored by defender Charlie Brooks.
Boston: Austin Barker, Ryan Makings, Finley Hipkin, Charlie Brooks, Kirils Snikeris (Daniel Bridges 80), Sean Bray-Smith, Jake Thompson, Rueben Fogg, Will Pettitt (Oliver Callaby 70), Toby Cotton, Rhys Smaller.