Get csv field values
You can use this format to achieve what you described:

http://api.thingspeak.com/channels/(channel_id)/field/(field_id).(format)


Source: http://community.thingspeak.com/documentation/api/

Edit: It seems that there are no available options that can do what you want. But, you can tweak the response like in this example:

  int i;
  String response = "created_at,entry_id,field2 2015-10-22 19:30:00,14878,5";

  for (i = response.length()-1; i &gt;= 0 ; i--)
  {
    if (s.charAt(i) == ',') break;
  }
  String value = response.substring(i+1);
  Serial.println(value); // This will show only 5