I did this on the first challenge, after several tries. This one lacks any special baddies, so you can just focus on repeating the same moves. Don't bother with the fancy stuff, just do simple hits and counters. Never do a ground takedown, it leaves you too vulnerable.
One trick you could try is purposely reducing your computer's performance. This gives you increased time to react and counter or choose a target. Just leave a few other programs running. MS does not consider this cheating. At this time, TA does not consider this cheating. Some users consider this cheating.