redirect sharepoint site collections with URL rewrite

we are migrating off SharePoint 2010 to 2013 I need to redirect site collections as we migrate.

2010 webapp and site collections
http://sp.mycomp.com/spsc1
http://sp.mycomp.com/spsc2
http://sp.mycomp.com/spsc3

we have finished migrating the spsc1 site collection to the 2013 farm

2013 webapp and site collections
http://newsp.mycomp.com/spsc1

I added a rule in URL rewrite to redirect
http://sp.mycomp.com/spsc1 to http://newsp.mycomp.com/spsc1

And it works great. The issue is, while that collection is redirected as
expected and we can still navigate to the root http://sp.mycomp.com we can
no longer reach the sitecollections that haven't been migrated. the browser just
grinds and never goes anywhere. How can I redirect just specific collections while lettings the others flow through as before? Help please!

Regards,
Ken