Albion retained top spot in the Sky Bet Championship with a resolute 1-0 win at Middlesbrough.
Hal Robson-Kanu, who signed a contract extension on Friday, was the late hero for the Baggies - stepping off the bench to coolly put the visitors in front with just eight minutes remaining.
Albion were scintillating at times but it is perhaps their mental and physical strength for which their victory on Teeside will be remembered.
The Baggies started strongly and had the majority of the early possession and opportunities. Filip Krovinović saw his shot blocked at close-range following good build-up from Grady Diangana, and Matheus Pereira couldn’t keep his effort down when in space soon after.
But Boro rallied and the Riverside got going around the 20 minute mark, with Sam Johnstone superbly denying Paddy McNair from range before Lewis Wing smashed wildly over.
Albion held firm, though, and came through the home side’s spell of pressure to get back on the front foot. Jake Livermore was unfortunate to slice wide and Diangana couldn’t quite guide his header on target following a dangerous Pereira corner.
The Riverside paid tribute to Rob Spray in the 32nd minute following the devastating passing of the Albion supporter in Bulgaria earlier this week.
There was one final close call for Boro with half-time just around the corner - Johnstone keeping out Britt Assombalonga before Kyle Bartley bravely cleared George Saville’s rebound off the line.
The break came and went, the weather got significantly worse on Teesside, and Albion picked up where they left off; Pereira denied a spectacular goal when Darren Randolph saved his bicycle kick.
The Baggies were dominant with the ball yet had to remain alert as Johnstone was at his very best again to block Saville’s low shot.
Bilić made a double substitution on 62 minutes and it very nearly paid off straight away as Kyle Edwards went through on goal - but was tackled at the very last second by Boro defender Marvin Johnson.
The Albion boss did see his other change win him the game, though, as Robson-Kanu was on hand to tap-in following a goalmouth scramble with just eight minutes left to play.
And to top off a memorable afternoon on Teeside, Ahmed Hegazi made his first appearance of the season from the bench in stoppage time, after recovering from ankle surgery.
ALBION: Johnstone, Furlong, Bartley, Ajayi, Ferguson; Livermore (Hegazi 90), Sawyers; Pereira, Krovinović (Edwards 62), Diangana; Austin (Robson-Kanu 62).
Substitutes: Bond; O’Shea, Townsend, Brunt.