Scotland was named player of the month for February on Tuesday
Jason Scotland fired Swansea into the play-off spots with his 50th goal for the club, a 77th-minute penalty.
The Swans, buoyed by Darren Pratley's return, dominated a blank first half.
Romain Larrieu's fumble of Tom Butler's cross broke the deadlock, Jordi Gomez beating the Plymouth keeper to the ball and going down under his challenge.
Scotland, named February's Championship player of the month on Tuesday, sent Larrieu the wrong way with the spot kick for his 21st goal of the season.
Swansea have now gone seven games unbeaten at their Liberty Stadium home.
Swansea manager Roberto Martinez: "The position we are in is a reflection of this performance.
"It was the determination of the players to get into that top six.
"You could see the goal was coming but all credit to Plymouth, I thought they were outstanding.
"Jason Scotland's 50 goals for Swansea City is a huge achievement in a very short period of time.
"You can see the fans love Jason, he loves it here and it's a marriage that works."
Plymouth Argyle manager Paul Sturrock: "I'm disappointed, I don't think we deserved to lose the game.
"The players feel the penalty wasn't a penalty. I would have to look at it. The referee took a long time deliberating before awarding the penalty.
"I can't believe there were nine bookings, six for us. He was inconsistent.
"The boy [Ashley] Barnes had a chance after two or three minutes and it would have put a different complexion on the game."
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