Use CURL

Do this

     $curl_connection= curl_init('http://mysite.com/index.php');
     curl_setopt ($curl_connection, CURLOPT_POST, 1);
     curl_setopt ($curl_connection, CURLOPT_POSTFIELDS, "option=com_content&task=blogcategory&id=24&Itemid=55"); 

or do this

     $post_data['cmd'] = '_xclick';
     $post_data[''] = '';
     $post_data[''] = '';
     $post_data[''] = ;
     $post_data[''] = ;
     $post_data[''] = ;
     $post_data[''] = ;
     foreach ( $post_data as $key => $value)
     {
          $post_items[] = $key . '=' . $value;
     }
     $post_string = implode ('&', $post_items);
     curl_setopt($curl_connection, CURLOPT_POSTFIELDS, $post_string);

     $result = curl_exec($curl_connection);
     curl_close ($curl_connection);