The Pilgrims were trailing in the northeast when Zaluzinskis and Horne scored in the 77th and 84th minutes respectively to preserve United's unbeaten away record so far.
The result left the teams fourth and fifth respectively in the early National League U19 Alliance Academy Division North table.
Boston: Cameron Fox, Ellis Perry-Burdett, Oliver Fields (Nathan Bowen 46), Will Langford, Finley Ging, Taylor Jaine (Charlie Brooks 46), Jake Henderson (Rueben Fogg 57), Kris Zaluzinskis, Luke Horne, Joe Wilkinson (Lucas Turrell 57), Josh Doran.