On a toxic night that ramped up the pressure on head coach Valerien Ismael and his players, goals from Emil Riis Jakobsen and Cameron Archer saw the visitors earn a convincing victory.
Before kick-off, it was revealed Ismael had omitted Sam Johnstone from his squad for an "internal issue" with the Express & Star understanding the England's international's absence was not injury or transfer related.
And things went downhill from there with the Baggies creating next to nothing all night and also failing to retain possession and make simple passes.
That led to boos and a mass exodus at The Hawthorns - with thousands of fans leaving the ground after Preston's second goal.
And Ismael said he understood that reaction.
"We understand everything," the boss said.
"We accept it. I take my responsibility and when we see something like that, the fans 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.
“After the win on Saturday we had a chance to move up the table and every chance we’ve had that, we’ve missed it.
“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."
Johnstone's omission before kick-off was a big shock with the glovesman expected to come straight back into the side having served a three game ban following his red card against Cardiff.
On the goalkeeper's absence, Ismael said: "We had an issue internally. It is solved now.
"But that is the reason he wasn't in the squad and won't be on Saturday (at Millwall) but after that he will be back."
Asked if Johnstone's omission impacted Albion's performance, the boss said: "As I said it's no excuse for us.
"We cannot afford to find excuses to drop into victim mood.
"We have no excuses for that performance, we are professional, we meant to put in a performance.
"We have standards we expect to see and tonight we didn't put in the performance."