The Premier League new-boys were without new signing Rio Ferdinand at Brisbane Road and they fell behind after just 10 minutes.
Romain Vincelot glanced a superb header from Dean Cox's cross past QPR goalkeeper Rob Green to put the League One club ahead.
That goal was just reward for a strong start from the hosts but a moment of top-flight quality from Hoilett - making his first appearance of pre-season - brought Harry Redknapp's side level after 19 minutes. The former Blackburn Rovers man found some space around 25 yards from goal and gave Gary Woods no chance with a shot that arrowed into the bottom corner.
QPR began to control proceedings thereafter but Green was forced into a fine double save to keep them level at half-time.
And Orient were undone shortly after the restart, as Barton fired home a free kick to put the visitors into the lead.
However, Cox snatched a draw for Orient late on as he wriggled free in the box before slotting home.