Learn from losses. Every loss is an opportunity to analyze your weaknesses and improve upon it.
Learning opportunity. Ok, I'm not a psychologist, but I do compete in sports. I look at losing as an opportunity to see what I need to work on. I think you can sometimes learn more about yourself when you lose than when you win. I'd suggest focusing on using your losses to figure out what the other person or team did better, and then working on that. And remember that no one wins all the time!
Acceptance. Sports is funny that way in that we can be better, play better, and still not get a result. Keeping a learning model in mind and a goal for improvement helps. Were you going to win everytime???