Training for will power?

I don't know if it's possible, but I want to find a training exercise that teaches how to stay focus when I'm physically tired. Often, my body has not yet been pushed to it's limit before it starts to shut down my mind.

I have noticed these recent weeks since my conditioning dropped that I have a hard time maintaining a rhythm in my movement, coordination, and intensity. It might be the drop in intensity brings about lapses in movement and coordination, but the key for me is to find a way to block out the distraction I feel from physical fatigue. It's as if my body starts to talk to my mind and says, 'don't look at the ball, you really rather wait until it comes to you so you can conserve your energy.' With this distraction, the intensity simply fades away. The sharpness in my seeing the ball goes with it. I start to have lapses in concentration when I don't really see and feel I'm playing at all. During these times, I don't see what my opponent is doing, where he's standing and how he's swinging and hitting the ball.

I will start looking for a training regiment that specifically addresses this problem (aside from the mental toughness training).