When I studied martial arts, our knife instructor told us that if you have to defend against a knife, just know that you WILL get cut. There’s no avoiding it. You just have to make sure you don’t get KILLED.
For immediate openers if you can, make a slice across forehead. Gushing salty blood will blind them. If you miss you may catch an eye instead which is okay too. Just a suggestion.
Yep, in a knife fight, two people are going to the hospital, and most likely one of them in a bag.