If, like me, you have the problem that your life regen is rather high, try this:
1. Set your blood skill to be Blood Rush.
2. Unequip *all* of your gear.
3. Engage in combat with Diablo.
4. Instantly requip your gear.
5. Assuming that you're high level, this will instantly drop your health below 10%.
6. Hit Blood Rush.
7. Watch as your health regens.
8. Kill Diablo.