The young Pilgrims’ good recent form went out of the window in a below-par defeat against Cheltenham Town on Saturday.
Things looked to be going perfectly to plan early on, as Argyle took a fifth-minute lead through Oscar Massey, after good work down the left from Rhys Shirley.
The Robins were level 10 minutes before the break when a cross from the right was volleyed home at the far post.
Cheltenham made it 2-1 on the hour with a fine 20-yard free-kick that flew over the defensive wall and into the top corner of the goal.
The scoring was completed 10 minutes later when a ball in behind the Argyle defence saw a visiting striker round goalkeeper Tyler Coombes before steering the ball into an unguarded goal.
Argyle will next travel to Devon rivals Exeter City on Saturday for the first fixture in a new regional competition, formed to reduce travel requirements during the coronavirus pandemic.
Argyle: Tyler Coombes, A Trialist (Oscar Halls 75), Oscar Rutherford, Ethan Mitchell, Brandon Pursall (Ali Mansaray 75), Jamal Salawu (Jack Endacott 65), Carlo Garside (Jeffery Forkuo 75), Charlie Miller, Angel Waruih, Oscar Massey, Rhys Shirley. Substitute not used: Lewis Moyle.