The key was to treat Horus like a human when he was attacking and a beast when he was being attacked. His fighting style had clear origins as if he was taught by some discipline when he was young, but his actual level was still rudimentary as if he hadn't properly learned since his childhood ended.
It was relatively easy to create openings in his stances. If he wasn't given the opportunity to attack, Atlas knew that he still had the advantage despite how things looked.
Boom! Boom! Boom! Boom!
Atlas had roughly three-quarters of his qi remaining. Instead of conserving it, he used it incessantly on Exploding Runes.
Horus was unable to get anywhere close to him exactly for that reason. Atlas was constantly moving around and avoiding any possible long-range attacks. At the same time, the waves of pressure spread by the explosions didn't let Horus proceed forward or move much at all.
Within that chaos, Atlas found his opportunity.
