Romain Esse scored the decisive goal to push Millwall towards mid-table and inflict another away defeat on Plymouth.
Argyle manager Wayne Rooney would have spent his evening wondering how his side could be so dominant in possession for large parts of the game, yet have nothing to show for it.
The Lions clinched their victory thanks to a 13th minute goal from attacker Esse.
His finish came from 15 yards out after he dispossessed Bali Mumba, drove forward and exchanged passes with George Honeyman. It proved enough to take the three points.
There was early drama when a first-minute Plymouth attack was ended by a clumsy challenge on Mustapha Bundu in the home side’s penalty area.
Referee Sam Allison pointed straight to the spot, only to realise the assistant official had already flagged for offside.
Millwall did not have long to wait for their opening.
Mumba dithered on the ball and was dispossessed by Esse, who found Honeyman on the right. He cut the ball back for Esse to drive into the bottom right-hand corner of Daniel Grimshaw’s goal.
Plymouth should have been level four minutes later. Ryan Hardie got between Millwall’s centre-halves only to direct his header straight into the hands of Lukas Jensen. Either side of the goalkeeper, and it would undoubtedly have been 1-1.
Esse was full of confidence following his early strike. The 19-year-old tried his luck with a long-range effort just before the half-hour mark and was denied by Grimshaw.
Millwall should have doubled their lead in the 51st minute. A stunning pass from Japhet Tanganga fell into the path of Femi Azeez, who had timed his run to perfection
The winger powered towards goal, with just Grimshaw to beat. His first touch was poor, allowing Plymouth’s defence to race back and desperately scramble the ball away.
The game petered out as the second half wore on, with the visitors unable to draw on any inspiration to trouble the Lions.
It is a result that leaves Plymouth with the worst away record in the Championship with just one point to show on their travels and four straight defeats.
They sit two points and one place above the relegation zone in 21st, while Millwall climb to 13th.
Millwall boss Neil Harris told BBC Radio London:
"We played so well at times. This season we definitely haven’t had the points return we deserve and the supporting stats show where we should be in the league, and how good our goal difference is.
"Tonight we weren’t as good as we have been in previous five home games, but the result was the most important thing.
"It was a step forward. It is a positive evening and goes to show what a strong point it was to come from behind at Derby and we take that confidence and momentum to south Wales (Swansea) at the weekend."
Plymouth boss Wayne Rooney told PA Sport:
“We should have had a penalty. Again another decision which is against us.
“I asked the fourth official why the referee gave it and then changed his decision. He said Callum Wright passed it back into Mus (Bundu), who was offside.
“But it’s quite clear Callum didn’t pass it back. A Millwall player played it back into Mus. So it’s not offside. Again it’s these small decisions.
“The referees are always honest with us and the feedback we get, and we’ve had it the last few weeks now, is when they’ve made a mistake. I’m sure we’re going to get that feedback after this game.”
(On his team's performance) “I’ve said to the lads every attacking player who entered the field tonight wasn’t good enough.
“We didn’t create anywhere near enough today, we didn’t hold the ball up, we didn’t run in behind, so that’s disappointing.”