How to disable additional desktops?

This keeps happening and is pretty rage-inducing. I will be playing a video game and I'm guessing I will accidentally press tab+something. The games open window will disappear and will be replaced with a second desktop. Different background, no windows open. It really sucks since I don't know how to get to the original desktop, so this has caused me to drop out of competitive games.
How do I disable this feature?

Regedit will do it (I want to but haven 't yet) Disable Virtual Desktops and keyboard shortcuts on Windows 1x