Jake Livermore scored a dramatic 94th-minute winner as Albion claimed a last-gasp 3-2 triumph over QPR to record an eighth victory in their last nine away matches in the Sky Bet Championship.
Livermore pounced in injury time to convert Mason Holgate's low cross from close range and seal all three points in thrilling style, sparking celebratory scenes in front of Albion's travelling faithful.
The winner capped a spell of late pressure from the visitors having twice been pegged back by the R's at Loftus Road.
Jefferson Montero, making his first start for the club, bagged his maiden goal after just five minutes, although Luke Freeman levelled for the hosts before the break.
Fellow January loan signing Jacob Murphy restored Albion's advantage just after the hour mark with a well-taken low finish.
Yet substitute Tomer Hemed converted a 75th-minute penalty to seemingly ensure the spoils were shared in west London before Livermore popped up with his first goal of the season to secure victory.
The triumph extends in-form Albion's stunning away record since early November, with promotion rivals Sheffield United next up on Saturday at The Hawthorns.
Albion showed three changes from Saturday's derby victory at Aston Villa, Montero, Sam Field and Stefan Johansen recalled.
Matt Phillips also made his eagerly-awaited return from injury to take his place on the bench.
And it was the visitors who got off to a dream start.
Mason Holgate and Johansen worked well down the right to set up Murphy, whose shot was cleared off the line and Montero was on hand to convert the rebound from 12 yards.
The Baggies were in control and passing it around confidently as they looked to work an opening, although clear-cut chances were few and far between after the early opener.
And it was the R's who levelled with their first shot on target in the 35th minute.
Johansen was caught in possession in a central area 30 yards out and the ball broke to Nahki Wells, who fed Freeman and he drilled home.
QPR goalkeeper Joe Lumley produced a super save to deny Kieran Gibbs in the 42nd minute as the scores were level heading into the half-time interval.
Wells and Pawel Wszolek sent efforts narrowly off target at the start of the second half.
Hegazi made a fantastic last-ditch challenge to block from Wells, before the Baggies retook the lead almost immediately at the other end.
Murphy collected Joel Lynch's poor headed clearance, skipped past his marker on the edge of the penalty area and drilled a low effort beyond Lumley and into the far corner.
However, the hosts drew themselves level once 15 minutes from time when Craig Dawson was adjudged to have upended R's frontman Hemed in the area, and he picked himself up to convert the resulting spot-kick.
Both sides had chances to claim all three points - Murphy for Albion and sub Ebere Eze for QPR, twice each - with Phillips stepping off the bench for the final 10 minutes and himself going close.
Yet it was Livermore who had the final say deep into injury time to send home happy the 1,492 travelling Baggies supporters.
Albion: Johnstone, Holgate, Dawson, Hegazi, Gibbs, Livermore (c), Field (Phillips 81), Johansen (Barry 65), Murphy, Rodriguez, Montero (Harper 57).
Subs: Bond, Adarabioyo, Bartley, Edwards.