Carlisle United took the challenge to their illustrious Championship hosts at Loftus Road and they earned their reward when a late Jason Kennedy winner booked their place in the third round draw following another extremely entertaining display.
The game started at a frantic pace with scrambles at both ends as QPR defended a corner, then a Miller cross, and then went on a break. A long ball forward found Carlisle light at the back but a deflected shot was eventually hooked clear as Polter tried to make it count.
The first real chance of the night came on 4 minutes when Hoilett found himself with space. He cut inside and dragged a tame shot at Gillespie as he went for glory with his left boot.
The R's were incisive as they built patiently with Polter and Gobern instrumental in unlocking a route down the left flank. A reverse pass appeared to leave Polter with a clear sight but his touch was heavy and the keeper was able to bring the move to an end.
United had their moments and a low cross from McQueen had to be picked up by Smithies at the near post as it threatened to squeeze through the gap.
A moment of good fortune almost brought the first goal when a blocked Gobern shot spun nicely for Grego-Cox. He hit it sweetly on the turn and Gillespie had to parry as it angled for the top corner.
Emmanuel-Thomas was next to go close when he skipped past two challenges and strode into the area. He shot low, through legs, but Gillespie watched it all the way.
The Cumbrians weren't about to sit back and roll over and a touch from McQueen found Asamoah with his back to goal. He was pushed wide but he was close with a thundering shot which flew into the side netting.
Nice football from Carlisle took Brough to the edge of the area and a sliding challenge from Doughty earned him a yellow card and a nervous moment as Grainger lined the set piece up. The slightest of touches from Kpekawa was enough to take it wide for a corner.
The hosts enjoyed another good spell as Emmanuel-Thomas dropped deep and he set Hoilett on a run with a neat pass down the right flank. A whipped cross brought a touch from Gobern which sent the ball high and wide.
The best and worst of Seb Polter was then on show within a matter of seconds as a sublime touch took him away from Raynes and into a dangerous area. He had the width of the target to aim at but he was disappointed as his poor shot on the run flew off into the night sky.
A winding 20-yard run from Hoilett ended in more disappointment for the home fans as a miscued effort spun into the stands.
And the visitors made the R's pay for their timid attacking approach when they pounced on some hesitant defending. Balanta played the ball forward intelligently and that left Sweeney and Smithies to go head to head for possession of the ball. The Carlisle midfielder got there first and he kept his head as he lifted it over the advancing stopper before putting it on a plate for Derek Asamoah to find his first goal of the season with a side-footed finish.
The lead was quickly snuffed out as the hosts hunted in packs and picked up the pace as they approached the edge of the area. Emmanuel-Thomas didn't need to be asked twice and even a firm hand from Gillespie couldn't stop his volley from bulging the bottom corner.
Emmanuel-Thomas put another shot wide in time added on for the first half, and the hosts were a whisker away from edging in front with their first attack of the second period when a downward header from Hill shaved the outside of the upright.
It was good home pressure and Polter called for handball when he nodded a deep corner back into the mix via a touch from Dicker. It had to be cleared off the line as Doughty tried to finish it off.
Carlisle almost hit back in style when Brough spotted McQueen on the overlap. A cross turned into a shot which had to be touched onto the bar by Smithies as it curled wickedly and dipped late.
A long kick brought good control from Polter as he stood his ground and his dinked pass for Hoilett left the away shirts exposed. Gillespie produced his save of the season so far as he stayed big before dropping to his right to stop what looked a certain goal.
It was suddenly end to end and McQueen brought the best from Smithies when he turned inside and let one fly. The keeper had to recover quickly to stop Sweeney from prodding the rebound home.
There was chaos in the home defence when Smithies failed to deal with a Miller jump at a free kick, and Archibald-Henville looped his header at the empty net. The away fans behind the goal were ready to celebrate but Hill was on the line to make a vital clearance.
Polter stabbed a toe poke wide as the goalmouth action continued to flow, and United had to take care as Kpekawa made the byline and drilled the ball low. Joyce completed the clearance before Grego-Cox could slide in.
The Cumbrians stunned the home fans for a second time with just over ten minutes left to play when Derek Asamoah spun, 20 yards from goal, and took a looping route to the byline. Jason Kennedy spotted the danger and he was given the easy task of slotting it home from just six yards out when a low pass was placed on his toe.
The R's had men in the box for every set piece late in the day, and United survived a late penalty shout, but they weren't about to be budged as they held on to claim a fantastic victory from another very accomplished performance.
QPR - Emmanuel-Thomas (40)
United - Asamoah (37), Kennedy (79)
QPR - Doughty (22)
United - Sweeney (24)
Carlisle United - Gillespie, McQueen, Miller, Raynes, Grainger (Archibald-Henville 55), Brough (Ibehre 85), Balanta (Kennedy 72), Dicker, Sweeney, Joyce, Asamoah. Subs - Hanford, Hery, Rigg, Thompson.
QPR - Smithies, Furlong, Hill, Hall, Kpekawa, Doughty, Gobern (Comley 67), Emmanuel-Thomas, Hoilett (Luongo 72), Grego-Cox (Chery 83), Polter. Subs - Lumley, Perch, Phillips, Blackwood.
Referee - Mr James Linington
Attendance - 5,501 (458 away fans)