Knee to the face and then after he flies backwards or sideways, make sure the knife is out of his hand while he's about to go to sleep and then sink in a RNC to put him to sleep.
I've been in some serious street fights and bar fights where knives where involved and that's how I've always got through them. A good friend of mine was wasted and a guy pulled a knife on him while he was almost asleep from the beating. As soon as he bent down to get the knife from his boot, I landed a knee in his face and kicked the knife away, then locked in a RNC until the police arrived about 1 minute later. Plenty of witness's as well as a video of what happend from start to finish. The police didn't do anything to me except seperate me from that group because they didn't know what they were dealing with.