When the scorpion shattered the black flame emitted by Ji Dong with a punch, the outcome of this battle was already determined.
Indeed, from the beginning of the battle, Ji Dong was creating various scenarios, including his first strike that sent him flying by the scorpion. That indeed reflected the strength comparison between the two at that time, but with Ji Dong's current strength, there was no need for such a direct collision of magic powers. The reason he did so was to bewilder his opponent and make the scorpion feel her strength was far above his own.