Rory Fallon's strike was enough to give Plymouth a first home win of the season over fellow strugglers Forest.
Paul Gallagher twice went close early on and Fallon also fired a shot wide as Plymouth dominated before Fallon put Argyle ahead with an 18-yard shot.
Jamie Mackie also hit the woodwork for the hosts after the break.
At the other end only a couple of fine saves from Romain Larrieu denied Andy Cole and Chris Cohen an equaliser while Wes Morgan saw red for Forest late on.
Plymouth manager Paul Sturrock: "It was far from a classic but we got the result we wanted.
"It was the type of game that we were nervy because we wanted our first win and they were looking for their first away points.
"The players know the tempo that they have got to get to for the whole of the 90 minutes and the work-rate that is required.
"At least we got that today - the important thing was to get the three points and our first home win.
Nottingham Forest manager Colin Calderwood: "It was a bizarre, bizarre goal that changes the result of a very bitty game.
"There were no particular chances for either side and if you get through to half-time you think you might be all right, especially away from home and the game being that way.
"But it was just a summing up of some of the goals we have conceded this season
"They are happening at the minute. We are striving to get something away from home but we've not taken a point."
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