nginx configuration for Symfony and WordPress running alongside each other

I have a Symfony site at /var/www/mysite/symfony and a WordPress blog at /var/www/mysite/wordpress. How can I direct mysite.com/blog to WordPress and all other requests to Symfony? Here’s what I’ve tried so far:

server {
    server_name mysite.com;
    root /var/www/mysite/symfony/web;

    location / {
        try_files $uri /app.php$is_args$args;
    }

    location ~ ^/(app|app_dev|config).php(/|$) {
         include fastcgi_params;
         fastcgi_param SCRIPT_FILENAME $request_filename;
         fastcgi_index index.php;
         fastcgi_pass 127.0.0.1:9000;
    }

    location ~ ^/blog {
        root /var/www/mysite/wordpress;
        try_files $uri $uri/ /blog/index.php?$args;

        location ~ .php$ {
                fastcgi_split_path_info ^(.+.php)(/.+)$;

                include fastcgi_params;
                fastcgi_param SCRIPT_FILENAME $request_filename;
                fastcgi_index index.php;
                fastcgi_pass 127.0.0.1:9000;
        }
    }

    access_log /var/log/nginx/mysite-access.log;
    error_log /var/log/nginx/mysite-error.log;
}

With this configuration I get a ‘File not found.’ error when I visit mysite.com/blog. My nginx log file shows FastCGI sent in stderr: "Primary script unknown" while reading response header from upstream. I know it’s not an issue with my php-fpm set up as Symfony runs fine at my site root.

Where am I going wrong?