If running 5K-10K races are part of your training, you've undoubtedly experience the dreaded mid-run slow down characterized by a lack of focus and concentration - and associated slowing of pace.
Typically, when you start, you are very focused on your position, your breathe, your pace...but eventually you may find your focus drifting some 10 - 20 minutes into your race.
To combat this, build high-intensity focus into your pre-race training by running your intervals with ever decreasing rest periods. Start with the "standard 3 minutes, gradually decreasing to 2 minutes and then 90 seconds as your fitness level improves.
And during the race? Use a Garmin or other device that tracks your pace as you run and manage your pace as you did during training to avoid mid-race drift.