Their first goal came about because we didn't have Cabaye. Although Vuckic played well the game passed him by a lot meaning West Brom had time in midfield to pick a pass, which is dangerous given Odenwingie's pace and movement. I also think the second and third would've probably been prevented by Saylor.
The main problem is, as people have said, Perch and Collo are too similar. Perch has been playing well recently, he just isn't strong in the air. Both of them prefer the ball on the floor and I seem to remember Perch made a very well timed sliding tackle in our box in the first half. We'll fare better when Williamson is back as he is in the same kind of mould as Saylor, even if he isn't as good as him.