How to defeat the final three predators in the alien campaign on Nightmare difficulty?

Note: On Nightmare difficulty you have no checkpoints.

After fighting/slipping through the ruins you end up with a battle against a pair of predators before taking on a single predator.

I found several guides stating that you can defeat the predators by spamming the heavy attack button. I had moderate success with this method but could not get the timing right to keep the final predator in an endless loop of knockdowns.

Are there any alternative strategies beyond hoping the heavy attack combo lasts long enough to allow you to perform the final harvest?