Correct spelling, definition: acing is a derivative of the verb ace. To create a present participle/gerund, one must add the regular suffix -ing to the end of this word – the general rule is to add -ing to the verb. Although, when a verb ends in a silent -e, we drop the -e. Therefore, the correct form is acing and the incorrect one is aceing.

Definition of acing:
verb (present participle), serving an ace against in tennis
Jake aced his opponent 10 times.
If you’re asking about one person that’s acing it, it’s definitely John!

Incorrect spelling, definition: this mistake may come from the fact that the basic word for the present participle/gerund of this word is ace. When we create a new form, we add the suffix -ing to the end of the root. The thing is that if a verb ends with a vowel -e, this letter must disappear in the present participle/gerund. That’s why the correct spelling is acing, not aceing.

Incorrect spelling