To me, the word "over confident" implies, too much, usually to the point of becoming a negative influence- like being too cocky. taking winning for granted or resting on your laurels.
That's not to say, some cocky or overconfident players, especially in team sports where other players have influence, go on to win, and in a sense "justify" their confidence, but I can see you viewpoint, too.
They have such an extreme form of confidence, that it seems beyond our understanding or comprehension- to the point of being "over."
Michael Jordan knew those last-second shots were going to go in.