Note* This only needs to be done if you have 2 or more articles in a folder.

Go to Admin > Publishing > Folders

Right Click on the Folder and select Edit Folder

Under Display Settings

Choose the article under the default article drop down list

Save

Done.

Note: If the default article is still not showing up, check to see if the article that is showing up contains the same user friendly url as the folder.

If this is the case please change the user friendly url of the folder.