The R's looked set to propel themselves into the top half when Heidar Helguson netted for the fourth successive Premier League match.
The 34-year-old's sixth of the campaign came after 20 minutes when he headed home a superb first-time ball from Joey Barton at the back-post.
Shaun Wright-Phillips thought he had doubled the home side's advantage moments later, although the winger's superb effort was chalked off for a tight offside call.
Neil Warnock felt aggrieved at the decision and saw his side fritter away numerous chances to extend their lead, allowing Long to level in the 81st minute.
Substitute Peter Odemwingie ghosted down the left flank and his superb cross was tucked away by Ireland international Long at the back post.
Heading into the match, the home side had been boosted by the return of skipper Barton from suspension, while Jay Bothroyd was also drafted in by manager Warnock.
Counterpart Roy Hodgson made one change of his own for the Loftus Road encounter, bringing in Graham Dorrans for the injured Zoltan Gera.
The Hungary international has been ruled out for the season after rupturing his anterior cruciate ligament, although replacement Dorrans looked lively in the opening exchanges.
Fellow Scotland international James Morrison fired in the first shot of the afternoon in the ninth minute, before Wright-Phillips and Barton had attempts of their own at the other end.
Neither managed to test West Brom goalkeeper Ben Foster, but counterpart Radek Cerny was being tested with regularity.
The third-choice QPR goalkeeper - playing due to injuries to both Paddy Kenny and Brian Murphy - thwarted a weak Gareth McAuley header before then doing well to stop a Jerome Thomas effort.
While West Brom looked slightly more dangerous going forward, it was QPR that broke the deadlock after a fine move in the 20th minute.
Jamie Mackie's mazy run in the box was halted by a fine tackle, but the ball fell kindly for Barton to loft a first-time ball to the back-post for Helguson to head home.
QPR thought they had doubled their advantage moments later when Wright-Phillips showed great technique to fire past Foster, although the winger's goal was disallowed for a tight offside call.
Despite the frustration, the west Londoners were playing with new-found confidence and Mackie came close with a long-range shot as the home side pressed with half-time closing in.
QPR continued in the ascendancy after the break and, having seen Morrison's calls for a penalty turned down at the other end, a lucky ricochet saw the home side come close to netting a second.
Barton controlled the ball after a blocking a clearance, played a neat one-two with Helguson and then curled just wide under pressure from Foster.
The match ebbed and flowed as West Brom began to assert themselves more, although QPR again came close during a penalty-box scramble involving Wright-Phillips, Mackie and Helguson.
West Brom were still in with a shout and Chris Brunt saw a long-range effort drift wide shortly after Foster almost gifted the Rs a second goal.
Armand Traore hassled the Albion goalkeeper, whose failure to make a simple collection would have been punished if Wright-Phillips could have directed home the left-back's cross.
QPR continued to press for an all-important second goal and were made to pay for their futility nine minutes from time.
Odemwingie outpaced Luke Young down the left flank and Long tucked home from close range at the back post.
The home side pressed forward in a bid to regain the lead, but were frustrated by West Brom's resolute defence and had Cerny to thank for stopping a late Brunt free-kick.