Nginx on front of node.js and apache

I have nginx running on port 80 with a proxy pass for multiple node.js instances.

I'd like to also use nginx on the same port, to proxy for an apache instance running on another port, say 8888.

Here's the basics of my nginx.conf

   upstream localhost {
           server 127.0.0.1:8000;
           server 127.0.0.1:8001;
    }

    server {
            listen       80;
            server_name  localhost;

            location / {
                proxy_pass http://localhost;
            }

            location /admin/ {
                proxy_pass 127.0.0.1:8888;
            }

    }

The two upstream's are node.js instances. But the /admin/ is for the site on apache, however it doens't work.

Is there another way to do this?

Thank you!