Not surprising given that QPR boss Harry Redknapp made nine changes to the side that drew 1-1 with West Ham last Saturday.
The Premier League hosts went behind when Armand Traore sliced into his own net from a corner after four minutes.
Dons keeper David Martin made several saves but his pass was latched onto by Ryan Lowe to double the lead, with Lowe then setting up Ryan Hartley.
Darren Potter rifled in to put the Dons out of sight with Jay Bothroyd and Fabio grabbing late QPR goals.
But he still included seven internationals in the team, as they were embarrassed by their opponents.
Three of the four goals they conceded came courtesy of defensive errors.
Another manager to rue his decison to play a weakened side, was Chris Hughton at Norwich.
Luton's Scott Rendell's hit a late strike that stunned the Premier League side as Luton Town became the first non-league team to knock a top-flight side out of the FA Cup since 1989.
Rendell's near-post effort with 10 minutes remaining capped off a monumental display from the Hatters.
Norwich missed decent chances through Grant Holt and Leon Barnett.
But Blue Square Bet Premier side Luton held firm after Rendell's goal to dramatically reach the fifth round.
Two sides that took no chances though were Everton and Reading. David Moyes played a first choice eleven at the Reebock and was rewarded with a late winner against the Championship side.
Reading raced into an early lead against Sheffield United when Noel Hunt nodded in from close range before midfielder Mikele Leigertwood made it 2-0 shortly before half-time with a fierce effort from distance.
Hunt grabbed his second with a scuffed effort from fellow forward Garath McCleary's cross.
McCleary scored a fourth with a well taken left-footed strike.
Aston Villa crashed out at Millwall on Friday night leaving only six Premier League sides definately in Round 5 - Man City, Arsenal, Everton, Reading, Wigan and the winners of Man United/Fulham. Spurs, Cheslea and Liverpool all face lower league opposition on Sunday. Even if they all win it only leaves nine Premier League sides left. Of the three, Spurs who face Leeds at Elland Road face the sternest test on paper.