She started her professional tennis career in 1999, and established herself as a major competitor in 2001, regularly reaching late rounds of international competitions. On June 7, 2003 she won her first Grand Slam tournament, the French Open, defeating her Flemish compatriot Kim Clijsters. On September 7, 2003 she won her second Grand Slam tournament, the US Open, once again against Kim Clijsters. She had reached the final after defeating Jennifer Capriati in semi-finals a mere 18 hours ago, during a terrific 3 hours and 3 minutes match.
On 19 October 2003 she achieved the first rank on the WTA list, taking over from Kim Clijsters. She was named the International Tennis Federation's women's singles World Champion for 2003.