Demon Hunter Class Mount

Greetings all, I am a Lvl 120 DH on the very last quest “To Fel and Back” where I have to fight the Fel Bat. Being a Lvl 120 he’s not even a problem, and THAT’s the problem. I kill him every time, whereas I am supposed to make him submit to me during each fight. I have tried everything, No weapons, no armor, low level weapons and armor. No spells, even hand to hand and I end up killing him.

I get to Phase 5 and kill him, end up having to reset the quest and start again…
How do I complete this and get my class mount???

Any help greatly appreciated and thank you!