Adel Taarabt struck in the opening minute at Barnsley to put QPR within touching distance of a long-awaited return to the Premier League.
The R's found the back of the net after 47 seconds, returning captain Taarabt tricking the Barnsley defence with a step-over and blasting beyond Luke Steele.
Both sides were lucky to end the first period with 10 men, Taarabt fouling Butterfield and receiving a yellow card, only for the Barnsley man to retaliate shortly afterwards and pick up a booking for his troubles.
Mark Robins' men might have gone in level at the break, Shackell failing to convert a header following Butterfield's cross as half-time approached.
With just over 11,000 at Oakwell, both sets of fans were in full voice as their sides emerged for the second half. The visitors cheered as Tommy Smith tapped in from close range on 55 minutes, but the goal was ruled out for offside.
Butterfield provided a late scare for the R's with five minutes remaining, his long-range effort rattling Kenny's post but Warnock's men return to London already dreaming about next season's away days.