Second half goals from Peter Halmosi and David Norris heaped more misery on the R's at Loftus Road.
The Hoops' winless streak in W12 extended to five matches, as Plymouth boss Ian Holloway guided his side to a memorable victory at his former stomping ground.
Halmosi opened the scoring four minutes into the second half, before Norris put the result beyond any doubt with a close-range strike on 62 minutes.
Earlier, Rangers came within a lick of paint of taking the lead in an even first half.
The recalled Danny Nardiello headed against the top of the crossbar, while Plymouth's best opening fell to Gary Sawyer, who saw his long range half-volley well held by Lee Camp.
After falling behind to Halmosi's strike, the R's were again denied by the woodwork courtesy of a Martin Rowlands free-kick, but it mattered little as Norris poached a second moments later.
John Gregory made a solitary change to the side that drew 1-1 at The Walkers Stadium four days earlier.
Nardiello replaced Ben Sahar in attack, with the Chelsea loanee dropping to the substitutes' bench.
There was no place in the 16 for another of the R's loan signings, Michael Mancienne, who was ruled out due to a back injury.
Argyle boss Holloway, on his second homecoming to W12, named an unchanged side, which meant in-form striker Sylvan Ebanks-Blake led the line alongside Barry Hayles.
In an entertaining opening, Plymouth fired the first warning shot, when Halmosi's 20-yard free-kick flew inches wide of Camp's left hand post.
Play switched immediately to the other end, where Nardiello - having been teed up by strike partner Dexter Blackstock - took one touch to set before forcing Luke McCormick to smother.
Nardiello was the key to Rangers' fast start and after a free-flowing R's passing move ended with the ball falling at the feet of the roaming Zesh Rehman, his pin-point cross was headed onto the top of the crossbar by the Welsh international.
Sawyer's speculative 40-yard strike from a half-cleared Plymouth corner kick brought the best out of Camp, while at the other end, Rehman - after linking up effectively with Nardiello - was denied by a last ditch save by McCormick.
The lively Akos Buzsaky curled a 30-yard free-kick a yard or so wide in the 41st minute, before the same player tried his luck again on the stroke of half-time, only to find the upper tier of the loft.
Rangers almost bagged an unlikely breakthrough in the second minute of added time, only for Moore to be denied by the sprawling McCormick, after Plymouth failed to clear their lines from a routine clearance.
The second half was only four minutes old when Argyle grabbed the lead, albeit against the run of play.
Gifted time and space on the left hand side of the R's 18-yard box, Halmosi cut inside before smashing a fearsome strike past the exposed Camp.
Having seen the woodwork deny his side in the first half, Gregory was again wondering what might have been on 55 minutes.
Marcel Seip pulled Nardiello to ground and when Rowlands stepped up, his sublime 25-yard free-kick left McCormick flat-footed, only for the crossbar to thwart the R's set-piece expert.
Sensing his side required fresh legs in an attempt to get back into the game, Gregory made a double substitution just before the hour, introducing Marcus Bignot and Hogan Ephraim at the expense of Rehman and Stefan Moore.
But it was Argyle who bagged the all-important second goal just four minutes later, when Halmosi headed the ball back across the face of goal and Norris smashed the ball past Camp from eight-yards.
Nardiello - easily Rangers' most tricky customer on an otherwise disappointing evening - fired over from an acute angle on 74 minutes, but it was Plymouth and Buzsaky who went closest to adding a third, when his 30-yard pile-driver flew wide.
Second half substitute Sahar should have opened his R's account when he was allowed to coast through unmarked after hesitancy at the heart of the Argyle defence, but the Israeli blasted over from 15-yards.
Late pressure from the R's saw Blackstock head straight at McCormick and Sahar denied by the Argyle keeper, but the first home league goal of the campaign continued to evade Gregory's side, who slumped to a fourth straight home defeat.
QPR: Camp, Barker, Cullip, Stewart, Bolder, Nardiello (Sahar 81), Blackstock, Rowlands, Moore (Ephraim 58), Rehman (Bignot 58), Leigertwood.
Subs: Cole, Curtis.
Plymouth Argyle: McCormick, Connolly, Nalis, Timar, Norris, Buzsaky, Ebanks-Blake, Hayles (Hodges 90), Halmosi, Sawyer, Seip.
Subs: Larrieu, Chadwick, Doumbe, Fallon.
Scorers: Halmosi 49, Norris 62
Bookings: Siep 54, Timar 77
Referee: A M Marriner
Attendance: 10, 850
