Crouch was getting into the danger areas without providing the finishing touch, and he was frustrated again with 15 minutes left as he headed Gareth Bale's cross off the outside of the upright as James scrambled to regain his position.
Sluggish Wales were shocked into life and had a penalty claim shrugged off after Gareth Bale had surged into the box only to be stopped, he felt, unfairly - but referee Aleksandar Stavrev disagreed.
And slack marking from Preston was punished when Crouch connected with Gareth Bale's cross to volley home off the post for the opener after 14 minutes.