I was reminded this weekend of the importance of breath control while racing. In many races our pace slows as we lose control of our breathing pattern, shoulders hunch, arms come up, rib cage lifts and diaphragm is restricted. This all results I'm laboured breathing.
When this happens mid-race, take a few strides to relax your shoulders and arms, breath out forcefully for a few breaths to drive your diaphragm up, then focus on your breathing, not your pace.
The tough thing is noticing when this is happening and remembering what to do about it.
It's also a great technique to relieve side-stitch.