I seek grammatical justification for "I did more than finish the job"

I see people say such examples as "I did more than finish the job", "He did more than win the game".

In such cases, "finish the job", which is a bare infinitival, occurs as the complement of "than". I wonder is there any justification in grammar for a bare infinitival to function as a comparative clause.

And what is the difference between such cases and those like "I did more than I finished the job"?