mydomain.com/wp-login redirects to wordpress.com/wp-login

You trying to change you .htaccess file probably look like this:

Note: Don’t forgot to clean your browser cache.

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule  /wp-admin/ /wp-admin/index\.php [L,P]
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress