Barnsley conceded another penalty when Shackell fouled Helguson and this time Adel Taarabt scored the spot-kick.
Bothroyd and Hogan Ephraim sent shots over the bar and Taarabt was then at the centre of controversy.
But Rangers refused to buckle and Taarabt fed Peter Ramage to pull one back with a powerful drive.
Taarabt produced another fine pass for Tamas Priskin to level things up and it was QPR who finished the stronger.
Taarabt, on loan from Spurs, argued with home fans, then stood in the centre circle asking boss Warnock to replace hm.
Adel Taarabt scored two minutes into stoppage time as Morocco claimed a 1-1 draw away to Togo in their Group A clash.
And Tommy Smith's header sealed the win from Adel Taarabt's classy cross.
And with the impressive Taarabt in their ranks - the former Tottenham midfielder ran Barnsley ragged - their ambition could come to fruition.
Skipper Taarabt was substituted before the hour mark but Rangers did not give up and Loach made good saves to deny Jamie Mackie and Hill.
After the break Taarabt and Priskin then combined for the hosts best chance of the opening period, but Priskin again failed to hit the target.
Adel Taarabt beat visiting keeper David Marshall, but saw his shot hit the post from 25 yards and Cardiff were relieved to see the ball ricochet for a goal-kick.
Then Taarabt turned on the style, setting up Ramage to fire a fierce first-time shot into the far corner before freeing Priskin to flash one home from 18 yards.
The leaders were now in command and Smith added a delicious second when his deft header from a delicious outside-of-the-foot pass from Taarabt found its way in at the far post.
QPR's mercurial forward Adel Taarabt had shown occasional glimpses of the brilliance with which he has illuminated the Championship this season and he was inches away from pulling a goal back with a curling free-kick.
Taarabt and Faurlin combined to create the first decent opening after the restart, with the skipper deliberately striking a low corner to his Argentine team-mate, whose curling effort drew a brilliant one-handed save from Loach.
Jamie O'Hara almost brought Tottenham a late reward, volleying Taarabt's deep cross narrowly wide from the angle, and Dimitar Berbatov forced a neat save with a drive, but it would have been ill-deserved after an uninspired display.
But they contested an open and entertaining game in the April sunshine at Vicarage Road, with Heidar Helguson crashing an inviting chance into the side netting inside the opening minute after a teasing cross from the ever-involved Taarabt.
Spurs boss Ramos mixed things up with 20 minutes left, replacing King with Adel Taarabt, but the hosts were indebted to a brilliant Robinson save on the stretch from Farfan's drive to keep them at least in touching distance.
The game changed decisively when Taarabt sprung into life to convert Smith's cross from the left with a precise finish and the Moroccan then went very close to a second goal with a curling strike that drifted the wrong side of Loach's goal.
Watford defender Adrian Mariappa made a sharp clearance after Loach had spilled a Taarabt free-kick, while Taarabt played a superb cut-back that picked out Faurlin, who had time to place his shot but wastefully drilled his effort over from 14 yards as the opening half ended goalless.
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