The skill-shot way is to dodge and then wait for his little stop animation. If you hit him in the back of the leg it'll do a temporary armor crack and then a second shot on that same leg within a few sec will kill it. you'll notice a little flame on his leg that indicates you've hit the first shot correctly.
But the other suggested ways are easier to time, especially if there's a lot of Chaos going on
Dominator is the business