Career
Johnstone was runner-up to Pat Serrett at the 1978 Australian Junior Championships. His best Grand Slam performance came at the 1982 Wimbledon Championships, where he had wins over David Schneider and Jay Lapidus, to make the third round. A right-hander, Johnstone made the finals in both the singles and doubles draws at the 1982 South Australian Open.
Singles: (2)
Doubles: (4).