A top international junior player, Immelman’s AJGA career was highlighted by a victory at the 1995 Polo Golf Junior Classic where he met and defeated Bubba Watson in the final, 2-up. The 1995 field foreshadowed Immelman’s future TOUR competitors including Ben Curtis, Carl Pettersson, Charles Howell III, Lucas Glover, Kevin Stadler and Matt Kuchar.
At the 1996 Rolex Tournament of Champions, Immelman placed third behind champion Howell and runner-up Bryce Molder. Later that summer, he finished eighth overall at the HP Boys Junior Championship, but won the 15-16 age division, beating the likes of Glover, Troy Matteson, D.J. Trahan and Jin Park.