Slaven Bilic has again told his Albion team to cut out the sloppy error after the Baggies' 3-2 victory over Blackburn.
Albion fell behind after just 25 seconds when a poor pass from Kyle Bartley put Romaine Sawyers under pressure and allowed Bradley Dack the chance to fire Rovers ahead.
After the Baggies had fired three first half goals, Sam Johnstone's error then gave Rovers another gift which Bradley Johnstone needed no invitation in taking.
"We deserved it, but we have to manage the game better. It was a bad 15 minutes - we didn't even start today and of course it affects us, that early," Bilic told Radio WM after the match.
"Fortunately we responded and then from the first goal until the end of the half basically it was excellent in every aspect of the game. Three-one should have been enough but we should have been even more up.
"Of course I'm not happy with their (second) goal, there were elements of a foul in it and it was a cheap one. We knew they were going to come fired up for the second half, they did and we had difficulty to control the game."