All I can really contribute is that this might be a major part of your problem. In training, preparation and review of your performance you should always have succeeding at the forefront of your mind, but when you are actually competing you should not be thinking about your opponent or how badly you want to win.
You just get in there, do your job to the best of your ability, and worry about everything else afterwards. I've played the best games of my life in rugby when all I've worried about is doing the "job" my coach told me to do. And I've gotten my biggest totals in PL when I've been completely oblivious to what my competitors totals are.
Afterwards, when you watch your match on tape or your coach tells you where you screwed up, be brutally honest with yourself, pick up everything you did wrong, worry about what your opponent did that gave you trouble, and figure out what you need to do to fix it - whether you won or not.
Getting beaten lets you know what you're doing wrong and gives you something to work with. It makes you a better player if you deal with it the right way. So don't be nervous about it.
Anyhow, thats my 2 cents. Hope it was at least slightly helpful!