Early in her career she represented Hong Kong (since the beginning until the end of the 1987 season).

Her best performance at a Grand Slam came when she got to the quarter-finals of the 1992 US Open, defeating Eva Švíglerová, Judith Wiesner, Jennifer Capriati and Helena Suková before losing to eventual champion Monica Seles.

After Hy-Boulais did it in 1992, Canada did not have another woman to survive into the second week at the French Open until Aleksandra Wozniak did it in 2009.

[1] Hy-Boulais represented her new country at the 1996 Summer Olympics in Atlanta, Georgia, where she was eliminated in the second round by the number one seed Monica Seles.

Hy-Boulais reached her highest ranking in the WTA Tour on 8 March 1993, when she became the number 28 of the world.