Bootcamp stuck in Windows

I have a Bootcamp partition with Windows 8.1 that I rarely use. Last night I was in OSX, closed the lid, and when I opened it this morning it was in Windows and I cannot get out.

• Booting with the option key down does nothing (still boots straight to Windows)
• Going to Advanced Boot Options in Windows shows Mac OS X as an alternative boot device, but when I choose it and reboot, it still goes into Windows.
• I've read that holding X on boot forces to OS X - never heard of that before, but also tried it with the same results as above.

I've reached the end of what I know how to do - other troubleshooting paths to take?

The Mac hardware stores the boot volume in NVRAM so you could power off the computer and then reset things by holding the Command Option P R keys down.

Once you've heard two boot chimes you can release things and if the Mac OS X volume is viable it will boot first. If that doesn't work then it's likely that the OS X volume has issues and the system is failing to boot there and falling back to the second viable OS - Windows.

You might be able to see that in the console if you boot verbose or single user mode.

The official fix at that point would be to boot into Recovery and then see about repairing or reinstalling OS X.

• OS X: About OS X Recovery - http://support.apple.com/kb/HT4718