Stop redirect to home page from rewritten url

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I have re-written a url in htaccess to point mysite.com/us/blog to point to mysite.com/blog
However instead of keeping the url the site redirects to mysite.com/blog.

the rule on the base htaccess is RewriteRule ^us/blog blog
and I have define('REDIRECT_TO_BASE_URL', false); defined in the site.config.

How can i stop the redirect to keep the alias url?