I did this in the UFC 189 into sequence. It's very easy if you just waste time as your not meant to loose this he get's very week at around 2 minuets left. What i did was take him to the ground waste time with endless transitions and then with about 30 seconds left go to Side Control he should give up his back go to Back side then Back Mount then Back Flat posture up and rain down fists and it will knock him out and your achievement will pop. If you have any questions please let me know and i can help out.