The Pilgrims trailed 2-0, 3-2 and 5-3 as they narrowly lost out to their title rivals.
Scott Floyd scored twice, while Jack Dykes and George Hobbins were also on target.
Boston (4-3-3): Harry Payne; James Gordon, Kofi Ross, Elliot Andrew (George Hobbins 12), Bailey Forth; Jack Dykes, Harry Vince, Oli Drummond (Jordan Tate 54); Scott Floyd, Tinashe Chavundura, Peter Evison.