A dour match exploded in last minute controversy as Plymouth snatched a draw through a Lee Hodges penalty in the fourth minute of stoppage time.
Swindon appeared to be handed all three points in a match ruined as a spectacle by incessant torrential rain thanks to captain Andy Gurney's 77th minute free-kick.
However, Argyle levelled matters when Alan Reeves was adjudged by referee Ray Olivier to have handled a right-wing cross when most people in the ground were convinced that the offending hand belonged to Plymouth striker Michael Evans.
Argyle gave a home debut to centre-back Tony Barras, allowing captain Paul Wotton to fill in for injured midfielder David Friio alongside Steve Adams and David Norris, who completed his transfer from Bolton before kick-off.
Swindon showed two changes from the side knocked out of the FA Cup at Oxford the previous week, with Andrew Gurney returning from suspension to replace Gareth Edds, and Steve Robinson coming in for Johnnie Jackson, whose loan spell from Tottenham had come to an end.
Creative football was impossible in a first-half played for the most part in driving rain and a fierce wind.
The home side came closest to opening the scoring just before the interval when Swindon goalkeeper Bart Griemink failed to grasp Lee Hodges' long-range shot but the ball slithered away for a corner.
The conditions eased a little in the second half but, with the pitch cutting up, the contest remained scrappy and Griemink had to be smart to thwart Barras after a goalmouth scramble.
Swindon replied immediately with Danny Invincibile playing in Eric Sabin but Argyle goalkeeper Romain Larrieu came of his line quickly to parry Sabin’s flick-on for a corner.
The sticky stalemate was broken 13 minutes from time when Plymouth conceded a free-kick 25 yards out on the right edge of the penalty area.
Gurney stepped up and beat Larrieu with an unstoppable shot into the top right-hand corner of the net.