Watch free-to-view highlights of Albion's Premier League clash with Liverpool.
Albion were edged out by Champions League-chasing Liverpool at The Hawthorns on Sunday evening.
The Baggies went in front thanks to Hal Robson-Kanu’s first of the Premier League campaign, but were pegged back by Mohamed Salah’s goal 33 minutes in.
And after a flurry of late chances, the visitors found their winner from the most unlikely source as their goalkeeper Alisson rose highest to head in a stoppage-time corner and seal all three points for the Merseyside outfit.
Sam Allardyce opted to make a couple of changes from last weekend’s defeat at Arsenal, with Grady Diangana coming in for his 50th Albion appearance and Robson-Kanu starting for the first time in the league this season.
Liverpool began strongly - Thiago saw an effort bravely blocked by Semi Ajayi and Nat Phillips headed over - yet the hosts grew into the contest and carved out opportunities of their own.
Ajayi twice nodded wide before the Baggies edged ahead on 15 minutes; the front two combining as Matheus Pereira flicked Robson-Kanu through to finish fantastically past Alisson.
Jurgen Klopp’s men might have equalised quickly after, though, when Sadio Mane missed a good chance from close-range, though they didn’t have to wait long to find a leveller - Salah side-footing home just after the half-hour mark.
And a matter of seconds later they almost took the lead, Mane’s back-heel deflected off Okay Yokuslu and into the path of Roberto Firmino to smash against the crossbar.
There were openings for both teams with an eventful first period coming to an end - Robson-Kanu had a shot blocked when in on goal and Johnstone saved Fabinho’s low strike - but it was 1-1 at the interval.
The Reds came out firing after the half-time break and thought they’d scored within five minutes of the restart, however Mane was judged to have been offside after poking in Salah's delicate cross.
Johnstone had to be at his best to deny the Egyptian forward when he took aim and Firmino hit a couple wide as Liverpool searched for a second - still Albion remained a threat and actually had the ball in the net next.
Kyle Bartley poked in after a corner had run through to him at the back post, but Albion celebrations were cut short after Matt Phillips was alleged to have blocked Alisson’s view in the build-up.
Trent Alexander-Arnold and substitute Gini Wijnaldum hammered late attempts off-target during the final minutes of regular time.
But then a corner deep in stoppage time prompted a rare and astounding moment as goalkeeper Alisson raced up for to meet the delivery, before guiding a header past Johnstone to win Liverpool the game in a crazy end to proceedings in B71.
Albion: Johnstone, Furlong, Ajayi, Bartley, Townsend; Phillips, Gallagher, Yokuslu (Livermore 75), Diangana (Maitland-Niles 73); Pereira, Robson-Kanu (Grant 81).
Substitutes: Button, O’Shea, Peltier, Gardner-Hickman, Robinson, Diagne.