Bolton centre-back Gary Cahill scored a goal any striker would have been proud of in first-half stoppage time to give the Trotters the lead.
QPR continued to punch their weight after the break before two goals midway through the second half finished them off. An own goal from Danny Gabbidon and a deflected strike from Ivan Klasnic sealed a first win in six for Bolton. The Croatian then set up Fabrice Muamba for a fourth 10 minutes from time. QPR defender Clint Hill was then harshly sent off with just seconds remaining.
To make matters worse, QPR look set to be deprived of the services of new signing Kieron Dyer when the injury-prone midfielder was stretchered off after just four minutes with a suspected broken metatarsal.
Dyer, signed as free agent after being released from West Ham in the summer, went to ground in an apparently innocuous incident and was carried off clearly in agony. He has now completed 90 minutes only once in his last 29 Premier League matches stretching back over the last three seasons. The 32-year-old was replaced by Orr.
The loss of Dyer came after QPR had the ball in the back of the Bolton net, only for the goal to be disallowed. Jay Bothroyd turned Adel Taarabt's cross goalwards, but fellow new Rs recruit DJ Campbell was clearly in an offside position when he steered the ball past Jussi Jaaskelainen.
Bothroyd had another chance to score QPR's first Premier League goal for 15 years when Gretar Steinsson sliced a poor clearance right into his path, but the Icelandic defender atoned for his error by deflecting the subsequent strike over the bar. That incident was symptomatic of an uncertain performance from the Trotters' defence.
Bolton were playing their way into contention, largely through the ever-willing centre-forward Kevin Davies, but again the home side could have been ahead when Taarabt - who was incisive and dazzling throughout - sent an audacious chipped effort high and wide.
As the half wore on Bolton continued to threaten, and they were rewarded in the second of five added minutes brought on by Dyer's injury. Steinsson played a short throw-in which was worked across by new Bolton signing Chris Eagles, and Cahill curled in a delightful strike right into the far top corner from outside the box that beat goalkeeper Paddy Kenny all ends up.
QPR began brightly after the break but as the second half wore on they lost a great deal of their earlier potency, allowing Bolton to press home the advantage.
They doubled their lead on 68 minutes when Eagles's low free-kick was turned past Kenny by Gabbidon, another QPR player making an ill-fated debut.
Just two minutes later it was all over for Neil Warnock's side when Klasnic's shot on the turn inside the area took a huge deflection off Orr and beat Kenny.
Klasnic turned provider 10 minutes later when he spied the run of Muamba and teed the England U21 midfielder up for a simple side-footed finish.
QPR's miserable day was wrapped up in injury time when Hill, already on a booking, got involved in a tussle with Petrov that garnered a second yellow card from referee Martin Atkinson, who seemed eager to set about beating his tally of 13 red cards last season as soon as possible.
The early signs do not look good for QPR, but the real test will be how they bounce back from this bitter disappointment.