French shotstopper Gilmartin has been missing since limping out of the 0-0 draw with Accrington at the end of January with a hamstring injury while Nelson, who also has a hamstring problem, has missed the last two games.
Gozie Ugwu made his debut as a late substitute in the win over Aldershot after recovering from an ankle injury which had sidelined the striker since he made the loan move from Reading.
Fellow forward Nick Chadwick misses out once again through suspension after his red card in early January.
Argyle, unbeaten in four, are in 20th position in the table, only two points clear of the relegation zone.
Pedro stepped off the bench to send Chelsea into the FA Cup semi-finals after they beat Leicester 2-1 at the King Power Stadium on Sunday evening.
RB Leipzig came from behind at the Red Bull Arena to end a run of four winless games and defeat Bundesliga leaders Bayern Munich 2-1 on Sunday.