There's a reason I will choose the side of the underdog in most situations. Look in their eyes. You don't see ego. You see their drive, their hunger & determination. You see someone who has observed and planned every strategic move they make. A human who has not only learned their opponents, but has mastered themselves. A true winner is never made out of comfort, they are carefully and painfully carved from the inside out.
Remember that when you feel like you're losing. If you can master yourself, then you should graciously accept the gift of being underestimated by outside ego. Because that my friends, is one of the greatest gifts an opponent can give you.