Late goals from substitutes Ben Gladwin and Michael Smith hauled Swindon back into the tie but it was not enough to keep Town in the competition.
Mark Cooper made five changes to the starting line-up that had beaten Leyton Orient on Saturday. Tyrell Belford replaced Wes Foderingham between the sticks while there were also starts for Jake Reeves, Anton Rodgers, Jack Barthram and Connor Waldon.
Just four minutes into proceedings, the Town found themselves a goal down. Argyle’s Lewis Alessandra burst clear of the visitors’ backline before striking the ball beyond Belford. Tyler Harvey went close for the home side moments later, lashing an effort that just whistled over Belford’s crossbar.
Swindon’s best chance early on came through Andy Williams. The striker anticipated a back-pass on the edge of the Plymouth box and nicked the ball away from the defender. His touch, however, let him down at the crucial moment and Argyle ‘keeper, Luke McCormick, was able to snaffle back possession for the home side.
Jack Barthram also spurned an opportunity, scuffing wide of goal after being played through neatly by Anton Rodgers.
With 22 minutes on the clock, Swindon were the architects of their own downfall again and Deane Smalley doubled the home side’s advantage. Town gave the ball away in midfield and Smalley profited, finding the back of the net.
Rodgers then went close from a free-kick but saw his effort plucked out of the air by McCormick.
Just before half time, things went from bad to worse for the Town as Alessandra grabbed his second of the night. Some neat trickery on the right hand side of the box opened up a yard of space which allowed him to steer a shot past Belford.
Early in the second half, Town’s first shot of note fell to Rodgers who drove an effort goalwards that was deflected behind by the defender. As the weather worsened and the rain fell ever-harder, substitute Michael Smith got a clear sight of goal after good work by fellow substitute, George Barker and Jake Reeves. Barker cut the ball back for Smith but the striker’s shot was easily pouched by the Argyle ‘keeper.
Town continued to press and, after Smith headed over from substitute, Ben Gladwin’s cross, Andy Williams fired in a shot that took a vicious deflection off a defender and looked to be heading in before McCormick intervened.
With twenty minutes to play, Town gained a foothold in the match thanks to Michael Smith. George Barker was tripped in the box and Smith stepped up to despatch the resultant spot-kick with aplomb, finding the bottom corner.
With their tails up, Mark Cooper’s men continued to press for another goal and Andy Williams volleyed over the bar while Ben Gladwin arrowed a long-range effort well off-target before Smith twice headed over the crossbar when well-placed.
As Town pushed higher up the field, gaps began to appear at the back. Reuben Reid barrelled his way through on goal but Belford got down well to paw away his goal-bound curling shot.
With minutes to play, Gladwin hauled Town further back into the match as his shot took a deflection before beating McCormick.
The Argyle ‘keeper would have the last laugh, however, producing a stunning save in stoppage time to keep the home side’s lead intact before Jack Stephens struck the post from inside the six yard box.