This question already has an answer here:
Wing-tip vortices only start occurring when the pressure difference on the two sides of the wing starts. Wouldn't this mean that by the time the downwash from the vortices is acting on the airflow it would already have bent on to the surface of the wing and could not be pushed down any more?
In this picture you can see that the flow is already on the wing and it can not bend down any further because the wing is there.
How do the vortices change the direction of the relative airflow before it reaches the wing? The vortices only occur on the wing so they should not be able to do this.
EDIT: When I say downwash I am talking about wing-tip vortices pushing the airflow down therefore reducing angle of attack.