Preston raised the pressure on Valerien Ismael as they ended West Brom's unbeaten home record with a deserved 2-0 win at The Hawthorns.
The hosts failed to register a single shot on target across 90 minutes and did themselves equally few favours defensively in a performance which saw them booed off at the end of both halves.
Greg Cunningham's deflected cross was turned in on the line by Emil Riis for the visitors' opener five minutes before the break.
Cameron Archer, making his debut after joining on loan from Aston Villa, rubbed salt in the wound against the Villans' West Midlands rivals by doubling the advantage 12 minutes after his entrance, when he nodded home the rebound after Allan Browne's effort was kept out by David Button.
Preston's faint hopes of reaching the play-offs were boosted after moving eight points behind Huddersfield in sixth, while West Brom missed the chance to close the gap on second-placed Blackburn to four points with their first home league loss since May 2021. Their evening was compounded with the news England goalkeeper Sam Johnstone had missed the game due to what Ismael confirmed was a disciplinary issue.
West Brom began at a high tempo, perhaps buoyed by their late show against Peterborough at the weekend, but soon found themselves unable to dominate a game where Preston were more than willing to let their own physicality do the talking.
Neither side had managed a shot on target in an attritional opening 40 minutes but there were still warning signs that Preston's opener may be coming, with Browne blazing over and Cunningham's pull-back from a free-kick saved by Button.
The Irishman would be involved when it did follow, with his cross touched by Cedric Kipre towards his own goal, playing Riis onside in the process and inviting him to tap home from close-range.
Ismael responded at the break, bringing on Taylor Gardner-Hickman, and the Baggies' tempo raised itself in the opening exchanges of the second period.
But it did not last. Matt Phillips' blocked shot was about as good as the hosts could manage before they were caught out as Preston flooded bodies forward. Browne's run was not picked up and allowed him to force Button into a save which fell kindly for Archer to nod home.
Any sign of a West Brom comeback, with their unbeaten home record now under severe threat, never materialised and instead the only thing which appeared to stop Preston threatening a third goal was their own contentment with the scoreline. They saw out the last 10 minutes with ease to only add to the chorus of boos which were aimed the home side's way come the final whistle.
What the managers said...
West Brom's Valerien Ismael: "We had a matter [with Johnstone], an issue in the squad and have solved the problem. He was not in the squad tonight and he will not be in the squad on Saturday but after that he will be involved. It will stay internal.
"I take my responsibility and when we see something like that performance, they have the right to boo and criticise. It was more than disappointing. I think tonight we deserved all the criticism we got and the disappointment and frustration because the performance was not there.
"We missed everything we wanted - it was a very strange feeling. We played with fear and we didn't recognise our team. It was a big disappointment. You can lose but we missed the basics of desire and passion and there's no excuse. We deserved to lose."
Preston's Ryan Lowe: "You've got to come to these places and believe you can win. West Brom is an intimidating place to come and they've got a wealth of money coming from the Premier League and they're trying their best to get out of this division.
"But we wanted to go toe to toe with them and the lads were fantastic. We nullified their strengths and worked on doing that over the last couple of days on the training pitch. West Brom try to drag you all over the pitch but I thought we were fantastic in not getting sucked into that."