Rory Fallon struck the winner against his former club as resurgent Plymouth claimed their third successive win at the expense of relegation rivals Swindon.
The win lifted Argyle above Paul Hart's Robins, who slipped to the basement, and the decisive blow was struck in the 10th minute.
Pilgrims goalkeeper Romain Larrieu started the move which led to target man Fallon sweeping home a cross from Yannick Bolasie.
Joe Mason could well have put the home side three goals clear by half-time, twice striking the woodwork.
His first shot from close range thumped back off Swindon Keeper Phil Smith's left hand upright and his second effort - from the right - beat the diving keeper from 20 yards but smashed off the far upright.
Argyle could have been made to rue those misses but their defence, well marshalled by experienced Larrieu, maintained a clean sheet.