United boss Dennis Greene opted to start with an unfamiliar XI and they were no match for a lively Forest side who led 2-0 at half-time courtesy of goals from Jorge Grant and Sancidino Silva.
Grant and Ilias Polimos added further goals after the break although the Pilgrims improved markedly as more senior players were introduced from the bench, eventually cutting the deficit three minutes from time when Scott Garner steered home Stefan Galinski's shot.
PIC: David Shipman.