DWIGHT Gayle bagged a brace as Albion hit four second-half goals to turn around a half-time deficit and triumph 4-1 over Reading at The Hawthorns.
Leandro Bacuna fired the visitors into a sixth-minute lead, which remained in tact until the interval, but a clinical second-half showing from Darren Moore's side secured a fifth succesive home league victory and extended their unbeaten streak to seven matches.
Dwight Gayle headed Albion level shortly after the restart before getting the final touch on Kyle Bartley's header to turn the game on its head.
Harvey Barnes, orchestrator of the late comeback at Sheffield Wednesday in midweek, added a fine third before Bartley, who had initially appeared to be credited with the second, did get himself on the scoresheet with an 80th-minute header.
It takes Albion's goal tally to 31 from 12 Sky Bet Championship matches and ensures Albion head into the international break on a high.
Johnstone was forced into an early save to parry away Saeid Ezatolahi's long-range strike but, from the resulting corner, the visitors took the lead.
Bacuna received a short corner and carried the ball into the penalty area before firing in off the far post.
Albion pressed for a reply and Barnes fired across the face of goal in the 18th minute, with Gayle inches away.
Marc McNulty dragged a chance narrowly wide for the Royals at the other end while livewire Barnes tried his luck from distance for the Baggies.
Both Jay Rodriguez and Gayle were thwarted by black shirts as they attempted pull-backs in promising positions, but it was Johnstone who was the busier of the two goalkeepers.
Yet, within four second-half minutes, it was all square.
Tyrone Mears sent a deep cross to the back post and Gayle was on hand to head home from a tight angle.
John Swift shot straight at Johnstone as Reading threatened to retake the lead.
But the Baggies took firm control within seven minutes.
Bartley headed Barnes' corner into the ground and, with Gayle getting the final touch, the ball bounced over Sam Walker and into the net.
And it was soon 3-1 as Barnes was sent clear by Rodriguez and unleashed a fine low finish into the far corner.
With 10 minutes to go, Bartley finally got his goal as he rose to meet substitute Chris Brunt's cross and head beyond Walker.
ALBION: Johnstone, Dawson, Hegazi, Bartley, Mears (Edwards 62), Livermore (Brunt 67), Barry (c), Gibbs, Barnes (Adarabioyo 88), Rodriguez, Gayle.
Subs: Myhill,Townsend, Hoolahan, Robson-Kanu.