A three-agent scenario is considered in 3-D Cartesian space, where a Pursuer aims at intercepting an Evader while the Evader aims to out-maneuver the Pursuer. A Defender working in cooperation with the Evader aims at intercepting the Pursuer before the Pursuer can capture the Evader. A proportional navigation strategy is implemented by the Defender and the Pursuer. The optimal control problem which strives at solving for the heading rate and flight path angle rate of the Evader is posed and solved. Using the even collocation method, the optimal controls for the Evader are found using a nonlinear program solver. An example is provided to illustrate the maneuvers made by the Evader to escape the Pursuer with maximum separation at final time.