Jefferson began his career as a substitute small forward for Keith Van Horn and showed great defensive skills and all-around ability. Because of his potential, and Van Horn's conflict with power forward Kenyon Martin, the Nets traded Van Horn to the Philadelphia 76ers and trusted Jefferson as a starter. Jefferson blossomed in the role, becoming a good mid- and long-range shooter in addition to his slashing ability. On August 13, 2004, Jefferson signed a six-year, $78,000,000 contract extension with the Nets.