Mame Biram Diouf (twice), Ryan Nelsen, Gael Givet and El-Hadji Diouf could all have given their side a comfortable lead.
However, the 20-year-old Hoilett showed them all how it should be done with a shot from the edge of the penalty area late in the second half.
The sparse crowd of 10,284 - 14,238 fewer than the one which witnessed the midweek Barclays Premier League victory over Liverpool - was given plenty of goalmouth action but had to wait until 14 minutes from time for the decisive finish.
At the heart of it for Blackburn was Morten Gamst Pedersen, who was the major creative force from central midfield and when he was not swinging in tempting crosses or firing in free-kicks he was prompting and probing in an attempt to find the one pass which would break down QPR's defence.
Hoilett, man of the match against Liverpool, also put in another positive display and eventually provided the killer blow which had been so lacking in everything previously.