I've counter killed and managed to do a few streak kills. I'm having some difficulty on the final Fight Club level. I manage to get up to the last dude but tend to have too few precious seconds remaining to finish him off.
Really, you just got to be quick at kicking and punching, time doing a counter attack and get back up on the first guy you started hitting. Always stick to one guy, never switch targets. It eats up time.
Also, at the start, throw sand into their eyes. It may allow you to trigger an instant kill on at least one of them (done this a few times).
"A great war leaves the country with three armies - an army of cripples, an army of mourners, and an army of thieves." ~German Proverb