it is not uncommon to start a competition feeling tired ! The quality of sleep you get the night(s) before is very important, and can be compromised by circumstances (sleeping in the truck, or waking up early ...) and by stress.
If you feel tired, you can try massaging what we call in Touch for Health® the "switching"points : http://www.touch-sport.fr/blog/video-points-de-switching/
The "tuning in" exercise (massaging your ears) can also help you regain focus : http://www.touch-sport.fr/blog/video-souplesse-et-mobilite/
I'm sorry the video are only available in French, but I'm sure you'll get the general idea.