Hayles struck deep into first-half injury time to cancel out Marc Nygaard's second goal in as many games.
And in a fiercely contested east-west London derby, both sides missed easy chances late on to take all three points.
The game kicked off to a frantic pace and after Danny Shittu was first to draw Andy Marshall into action, Nygaard broke the deadlock in the 26th minute with a free header from Lee Cook's corner.
Towering Danish striker Nygaard was loitering on the edge of the area but when Cook whipped in the corner he ran clear of Don Hutchison to leave Andy Marshall with no chance.
But Millwall hit back in first-half injury time with an equally easy header from Hayles, who powered in Carl Asaba's cross with the visiting defence left in tatters.
Hayles almost bagged himself a second with 11 minutes remaining with a shot that ricocheted of the legs of defender Georges Santos only to drift wide.
Ady Williams missed an easy chance late in the game when he headed Jamie Vincent's corner over the bar from four yards out.
Millwall were missing Jody Morris, who was suspended after being sent off against Cardiff, while QPR had to make do without Paul Furlong who saw red after scoring the winner against Leicester last weekend.
Shittu was first to trouble the home defence when he launched a header goalwards from Richard Langley's cross in the second minute of the game.
But Millwall were far more lively than in their dour 0-0 draw against Cardiff at the weekend and Asaba drew Simon Royce into a diving save with a low shot in the 11th minute.
Former Millwall midfielder Marc Bircham, whose every touch was booed by the home fans, was lucky to stay on the pitch after being involved in two tussles with Hayles in the first half.
Hutchison came close to scoring Millwall's second in the 69th minute after Phil Ifil had put the ball through, but Royce kept the ball out of his path with some brave goalkeeping.
Dean Sturridge, who has struggled with injury problems since signing for QPR last season, hobbled off with ten minutes remaining.