Sam Parkin celebrated his award of Swindon's player of the season by scoring the goal that ended Plymouth's flickering hopes of a second division play-off spot.
Parkin took his tally for the season to 24 with a sharply taken goal in the 68th minute as Plymouth threatened to equalise a first-half effort from departing Australian Danny Invincibile.
Swindon should have been ahead in the fourth minute but Stefani Miglioranzi headed against the underside of the bar from six yards when it looked easier to score.
Plymouth, well organised and methodical, came close to an equaliser with Marino Keith, David Norris and Lee Hodges all going close in a competitive first half.
Teenage goalkeeper Craig Farr made a promising league debut with important saves from Nathan Lowndes while at the other end the ever-dangerous Parkin shot across the face of the goal with only French keeper Romain Larrieu to beat.
Plymouth came desperately close to an equaliser in the 52nd minute when Lowndes took a pass from Keith, went around the on rushing goalkeeper but then saw his shot cleared from the line by the retreating Miglioranzi.
Parkin's goal came in the 68th minute when he ran on to a pass from Invincibile and held off a strong challenge from defender Graham Coughlan before shooting home via the inside of a post.
Swindon manager Andy King, free from relegation or promotion concerns, chose the occasion to give opportunities to Farr and local lad Ian Herring, who was making his home first appearance.
Herring marred a comfortable display with a second-half booking and later the Swindon manager sent on teenagers Chris Taylor and Dave Bampton to give them league experience.
As Plymouth threw players forward in a desperate attempt to snatch a goal, Swindon almost added more with Invincibile shooting against the legs of Larrieu and Junior Lewis, on loan from Leicester, forcing a save from the goalkeeper.