You just keep casting DC whenever it pops up. Just remember in a group setting your only job is to hold aggro...even if that means chain casting lvl 9 spells until you hate yourself.
Something I used to do is pull with clinging and DC before they get to the group. Then I would start off at the camp with DC close to being off cooldown. That way you get a jump on the aggro game even if you get hit a couple times on the way there. Later with mana to spare you can mix in heart flutter on the pull since it's a longer cast.
Knights hold great aggro but ultimately a DPS class has to meet them half way. If they can overwealm your ability, kudos...now they should reign it in
[You must be logged in to view images. Log in or Register.]. Later on it gets easier, they die quicker and rezzes aren't always available.