A battle between formidable martial artists was not just a fight of one's level and mystical abilities; it was also heavily dependent on battle tactics!
Battle tactics were not like mystical ability or secret arts; it was about one's technique. For example, one might feign weakness at the start and then suddenly counterattack and win with one strike. Or perhaps one might purposely reveal a 'flaw' that the enemy might think he could capitalize on, and then counter that move and kill the enemy instead!