A stunning solo goal and another from a Blues old boy brought reviving QPR a 2-0 win at Birmingham.
Hall put Rangers ahead seconds before the end of the first period with his third goal of the season.
He had seven games on loan with Blues from parent club Tottenham five years ago, prior to a permanent move to QPR, and that just made it harder for Birmingham to take.
They were picked off again in the 67th minute when Osayi-Samuel started from the halfway line and just surged past everyone.
Current Blues boss Pep Clotet is trying to fashion a team that is both easy on the eye and successful but on this evidence he has got a long way to go.
Rangers were also content to keep the ball and the result was a dull stalemate until Hall put Rangers into a lead that had not looked likely.
With Birmingham in their dark blue and QPR in a change strip of light blue, it looked like a version of the boat race and Rangers were first to stick their oar in.
Rangers had just ended a damaging run of seven games without a win by beating Preston on Saturday and were desperate to build on that.
They were under pressure again though in the 33rd minute when Birmingham's Jeremie Bela, signed from the Spanish second division, showed what a bargain he is with a turn of pace that took him past his marker and finished with an angled shot that flashed just past the far post.
QPR had not kept a clean sheet all season until Preston failed to score against them and Birmingham found it surprisingly difficult too despite dominating most of the game.
But only most of it. In a minute of added time Eberechi Eze lifted a free-kick into a bunch of players and Birmingham failed to deal with it.
The ball skimmed off Kristian Pedersen's head and out of the scramble Hall got the ball over the line from close range.
Clotet surprisingly took Bela off in the 53rd minute in a double substitution that also brought Lukas Jutkiewicz into the game.
It was a plan to try to offer something different to break down QPR but it did not work.
Osayi-Samuel stunned Birmingham with his solo goal, powering down the left in a tremendous run and bashing the ball into the net.