It can be hard to stay focused during a race. A big part of staying mentally strong includes achieving calm amid the mental 'storm' of pressure and expectation. The athletes who are successful at achieving goals and PRs perform well under pressure by staying in the moment. I find it helpful to focus on things like my running form, breathing, fueling and hydrating. These focus points can take the edge off the discomfort and fatigue that set in during the second half of a race. Setting a PR is never an easy task but it's often more in your head than in your legs.