Combat doesn't last that long. If you're ten minutes in and haven't beaten your opponent, you lost or you left.
When dealing with an entity as vast as a deity, something about that just doesn't seem right to me.
So look at it from the other direction. If a deity has been trying to directly outright murder one of more mortals, for the last ten minutes, and he hasn't succeeded, does that seem right to you?
Your 100 plus round combat isn't going to happen without a new special ability like "Arbitrary Fight Scene Extension (Ex):
Azathoth cannot be defeated for the first 100 rounds of any encounter. This ability is a specific exception to any abilities anyone else has that would allow him to be beaten. Azathoth cannot defeat anyone for the first 100 rounds of an encounter, either." If he's beatable, it will happen before Round 100. If he's not, he fails one of your wants and
he looks pretty silly taking that long to kill mortals he can't lose to.