In his junior career he partnered countryman Steven Downs and the pair were boys' doubles champion at the 1993 French Open and 1993 Wimbledon Championships.

They defeated the experienced pairing of Mark Knowles and Daniel Nestor in the semi-final and won the final in a walkover, after one of their opponents, Andre Agassi, withdrew with a shoulder injury.

Greenhalgh also made two Grand Slam appearances with Silcock, at the French Open and Wimbledon in 1999, failing to progress past the first round in either.

[3] He regularly represented the New Zealand Davis Cup team during his career, participating in a total of 15 ties.

His six doubles wins with Brett Steven makes them the most successful ever pairing for New Zealand in the Davis Cup.