How should a student defend his 1st authorship in front of his advisor politely and effectively?
In addition to Peter's answer, one should also keep in mind the accepted practices in one's field of study. For instance, in some fields, such as economics and parts of mathematics, alphabetical order is the default; in other areas, such as organic chemistry, the principal investigator of the lab—not the primary author of the paper—has traditionally been given the first spot in the list.

If you are in a field where the order is somewhat preordained, it's going to be very difficult to change that tradition, for many reasons. In such cases, you should optimize your placement within the "available" options.