Queens Park Rangers earned their first win under new boss Mark Hughes, and their first in the FA Cup for 11 years, as Danny Gabbidon's header proved enough to beat a spirited MK Dons.
Hughes' side struggled, with Charlie MacDonald shooting wide and Jobo Ibehre failing to turn in from six yards.
Shaun Wright-Phillips was denied when clean through as his shot was saved.
Then as the visitors looked most likely to score, Gabbidon turned in Wright-Phillips' corner to earn victory.
Luke Young could have made it safe when his shot was stopped by the impressive Dons keeper David Martin, but Rangers held on for their first win in 11 games.
And, although they stuttered to beat a well-marshalled Dons team, they have now earned a home tie in the next round against west London rivals Chelsea, who they have already beaten this season.
Dons boss Karl Robinson had reason to feel hard-done by on a night when his side underlined their smooth passing style, but his League One team can also take credit for running QPR so close over two games.
On the other hand, Hughes, who won the Cup four times as a player, will be content to end a barely believable run of QPR FA Cup defeats stretching back to a win over Luton in 2001.
But he will be well aware of the task ahead as he aims to build confidence in his team as they aim to secure their Premier League survival.
At times, the visitors were the better side and, to begin with, it was was only when they made any serious inroads that QPR seemed to respond.
Rangers were certainly not making the most of the occasional Dons errors as they passed it out from the back, and it was MacDonald who headed wide from the first serious chance.
Soon after, Wright-Phillips was stopped by a last-ditch tackle when he was played through and, from the resulting corner, QPR were denied a goal because of a push on the keeper as Shaun Williams headed into his own net.
Robinson's side then had a golden opportunity to take the lead when Stephen Gleeson's pass found MacDonald but he fired wide as he closed down on goal.
However, that miss was topped when Martin saved Wright-Phillips's effort when the winger was sent clean through by Akos Buzsaky.
It led to the vocal visiting supporters singing: "Premier League, you're having a laugh" and it was true that QPR had not found a rhythm which reflected the 31 places between the two sides.
Hughes picked 10 of the 11 players who had lost at Newcastle on Sunday, so there may have been an element of fatigue involved.
If anything, the Dons - who enjoyed a 10-day rest coming into this match after their weekend game was postponed - improved after the break, Ibehre somehow failing to make a connection from six yards following Adam Smith's whipped cross off the right flank.
MacDonald then nearly poked in Gleeson's shot on the hour as the visitors underlined how they had come within two minutes of winning the initial game.
Heidar Helguson, who had scored the late equaliser in that fixture, replaced Buzsaky, who had tested Martin with a wicked free-kick.
And, from the following corner, Gabbidon headed in Wright-Phillips' delivery for a goal against the run of play - his first strike for nearly seven years.
Young had a chance to settle it late on but, once Rangers scored, they kept possession and saw the game out as the Dons realised their best chances had been and gone.