In some cases, the default Mac utility may fail when unzipping your restore. In this case you will want to use The Unarchiver:
1. Visit http://wakaba.c3.cx/s/apps/unarchiver.html and click 'download'
2. Go to the downloads folder in Finder, and double click TheUnarchive.zip to unpack
3. Right click on the restore file, select 'open with' and choose 'The Unarchiver'. You can then create a new folder to place the restore in.