Querying the entry for an HTTP Referer craft.request.urlReferrer returns the full URL of the referrer, while craft.entries.uri accepts the URI only. 

Do I need to split the URL just to get URI path, write a twig filter, a custom plugin?

Maybe I can’t see the forest for the trees, but it seems like there should be an easier way.
No obvious solution sticks out to me using only native Twig functions/filters.

It'd be pretty trivial to write a custom filter using parse_url(), though...