Guard yourself. Take your shirt, your jacket, whatever you have. Maybe even a messenger bag or a purse. Give that dog something to go after. So that it's not going after any other vital areas of your body.
Take your shirt off, and put it around your arm. You want to protect your mainly where the ulnar and radius flow, 'cause that's where your major arteries are.' So if you're going to give a dog your arm, and give it the forearm. Not this side, 'cause that's where all your vital arteries are.'
Punch it in the nose, in the muzzle. Reason being the muzzle and the nose is going to be right there front and center. It's a big target. You can go for the eyes and some other areas of the body, but the reality is those are small targets. You want to go for big targets.
When you under stress, gross motor skills are about the only thing that are going to work. So that means big movements by you to big targets on the dog. Anything else, you'll probably miss and give the dog an advantage. Kicking it behind the arms, near the rib cage is also another alternative because it's very sensitive underneath their armpits, just like it is for us.
If you're going to fight, fight with vengeance, and try and make that dog understand that you are the alpha.