Mikele Leigertwood and Peter Ramage were both given their marching orders, as Rangers were undone by Aaron McLean's first-half strike for Peterborough United.
Despite a tight opening to the match, the Posh broke the deadline on as early as nine minutes when McLean fired George Boyd's cross into the net from close range.
The R's - and in particular the impressive Lee Cook, who made his first start in just under ten months - pressed for an equaliser throughout the affair, though their task was made all the harder in the second half.
First, Leigertwood was shown a straight red card with 30 minutes remaining when he was deemed to have gone in two-footed over the ball.
That was before Ramage was shown a second yellow card for a late challenge in the 82nd minute.
R's boss Mick Harford made no less than four changes for the visit to London Road.
New loan signings Marcus Bent and Tamas Priskin were brought straight into the side at the expense of Rowan Vine and Jay Simpson.
Meanwhile, Ramage returned at right-back in place of Akos Buzsaky, who had to make do with a place on the bench.
Cook made his first start since April on the left-hand side of midfield, replacing Adel Taarabt who missed out owing to the Football League ruling that only allows five loan players in a matchday squad.
So, with Carl Ikeme in the R's net, Ramage and Matt Hill occupied the full-back berths, with Matt Connolly and Kaspars Gorkss continuing their partnership in the centre of defence.
In midfield, Rangers skipper Leigertwood and Cook started out wide, with Alejandro Faurlin and Nigel Quashie in the middle.
Bent was joined by Priskin in attack.
Over 1, 500 Rangers fans turned out in force for the trip to London Road, and it was QPR who fashioned the first opportunity to score.
A misplaced pass from Craig Morgan in the Posh defence was intercepted by Priskin, who in turn touched the ball onto Bent around 25-yards out, but he could only drag his shot wide of the goal.
Play soon switched to the other end, where Peterborough raced into an early lead courtesy of McLean.
Craig Mackail-Smith fed Boyd on the right-hand side of the area, and he skipped past two challenges to square for McLean, who had the simplest of tasks to fire the ball home low from six-yards out.
Buoyed by their opener, the Posh were only prevented from adding number two by Ikeme, who raced out to the edge of his box to slide the ball away from Mackail-Smith after Boyd's cutting through pass.
Moments later, passes were exchanged between Tommy Rowe, Boyd and Chris Whelpdale before the unmarked latter found space to shoot on the right-hand side of the box, but he could only smash the ball high and wide of the goal.
Searching of an equaliser, Rangers then went on the attack at the other end. Ramage and Faurlin combined well to find Bent on the edge of the penalty area, before his shot was deflected over for a corner.
Soon after, Whelpdale found the ball on the right wing, and he cut in from the touchline before sending in a left-footed effort straight at Ikeme.
QPR then went their closest yet to finding the net. Faurlin, Priskin and Leigertwood exchanged passes before the latter fired in a low shot on goal that was gathered by Joe Lewis.
Moments later, Cook played a delicious free-kick into the area from the left onto the head of Connolly, but the defender could only head over the crossbar when under pressure from his marker.
At the other end, good work from Mackail-Smith down the right allowed him to centre for Rowe in the box, whose header went only inches over the goal.
Just before the interval, Quashie's cross into the box was headed back only as far as Cook inside the penalty area, but he could only drag his shot wide of Lewis' right-hand post.
Both sides struggled to create chances in a tight opening to the first ten minutes of the second half.
Rangers were the side that fashioned the first opportunity after the break though.
Gorkss' long-throw into the penalty area was cleared only as far a Connolly 18 yards from goal, and his driven shot was held by keeper Lewis.
Soon after, the R's were dealt a massive blow in their attempt to get back into the match as Leigertwood was shown a straight red card.
Faurlin's over-hit pass meant that Leigertwood had to stretch to retain possession, and in doing so he was adjudged by the referee to have gone over the ball and caught the legs of Rowe.
Mr McDermid wasted little time in reaching straight for his pocket, sending the R's skipper off at a key point in the match.
Now a man as well as a goal to the good, Peterborough continued to search for a second.
Mackail-Smith almost got it, finding space on the left-hand edge of the penalty area only to be denied by a fine save by Ikeme for Rangers.
Any hopes that the R's had of getting back into the affair evaporated with just eight minutes left on the clock.
With the R's backline firmly stretched, Ramage was forced into a late challenge on Rowe, resulting in his second yellow card of the match.
Rangers pressed for a leveller when substitute Hogan Ephraim went close late on, but he could only blaze over the bar.
Peterborough United: Lewis, Williams, Morgan, Lee (Simpson 46), McLean, Boyd (Frecklington 82), Mackail-Smith (McLeod 82), Rowe, Whelpdale, Bennett, Livermore.
Subs not used: Gilbert, McKeown, Geoghaghon, Reid.
Goals: McLean (9)
Bookings: Lee (45), Simpson (52), Bennett (83)
QPR: Ikeme, Ramage, Leigertwood, Bent, Gorkss, Quashie (Ephraim 57), Connolly, Cook (Vine 81), Faurlin, Hill, Priskin (Simpson 65).
Subs not used: Stewart, Buzsaky, Cerny, German.
Bookings: Ramage (73 & 82)
Red Cards: Leigertwood (60), Ramage (82)
Referee: Mr D McDermid
Attendance: 8, 933 (Away: 1570)
