Eduardo Vargas, Charlie Austin and a fabulous Bobby Zamora lob put Rangers 3-0 up at half time before Joey Barton's stoppage-time strike.
Albion disintegrated in the first half and, while Victor Anichebe pulled a goal back after the break, they could not fight back and had Youssouf Mulumbu sent off late on
QPR are now a point from safety and go to fellow strugglers Villa - who lost 3-1 at Manchester United - on Tuesday after ending a five-game losing run.
The Baggies are not safe yet, eight points above third-bottom Rangers, and host rock-bottom Leicester next week.
Vargas replaced Junior Hoilett for the visitors after his goal in the 2-1 defeat to Everton last time out and justified his recall after 15 minutes.
A quiet opening had seen little action before Austin flicked on for Vargas and the midfielder stepped forward to unleash a low 25-yard effort past Boaz Myhill.
Earlier, Brown Ideye - recalled after a knee injury - had nodded over when free at the far post and the Nigerian could have also equalised within four minutes when he directed Chris Baird's cross wide.
But the Baggies never recovered from Vargas' goal and rarely threatened Rob Green for the rest of the half.
Vargas was forced off after half an hour but it failed to slow the visitors who doubled their lead seven minutes later.
Baird and Darren Fletcher lost possession to allow QPR to break and win a corner and Matt Phillips' delivery was flicked on by Nico Kranjcar for Austin to nod in unmarked at the far post.
Shell-shocked, the Baggies buckled and conceded a third two minutes before half-time through Zamora's brilliant improvised effort.
There seemed little on when he edged ahead of Joleon Lescott on the corner of the box as they chased a long ball, only for the former England man to sensationally lob Myhill with the outside of his foot.
QPR, whose only previous away win this season was at Sunderland in February, had it too easy against the wretched Baggies who failed to turn up.
Anichebe replaced the ineffective Stephane Sessegnon at the break and Albion went close when Craig Gardner fired straight at Green after 54 minutes.
Austin then tested Myhill but Anichebe made it 3-1 on 58 minutes when he glanced in Saido Berahino's cross from eight yards.
Green then saved Ideye's deflected effort as the Baggies improved with Rangers increasingly relying on the counter attack.
And Berahino should have made it 3-2 with 13 minutes left when he nodded a sitter at Green after Anichebe's knockdown found him free six yards out.
But any hopes of a late rally ended on 84 minutes when substitute Mulumbu - who was on for just 12 minutes - was sent off after an aerial challenge with Barton.
And the Rangers midfielder grabbed a late fourth in stoppage time when Albion failed to clear under pressure from Austin and Barton rammed in from close range.
Source : PA
Source: PA