Widjaja's highest WTA rankings have been No. 55 in singles and No. 15 in doubles. She was the highest-ranked Indonesian player in 2004, and also participated at the 2004 Summer Olympics in Athens.
She became the first Indonesian to win a Wimbledon title when she defeated Dinara Safina (sister of men’s player Marat Safin) 6–4, 0–6, 7–5 to claim the junior girls title in 2001.
The same year she became the lowest-ranked and youngest player to claim a WTA singles title when she won the Wismilak Open in Bali before she turned 17. Her ranking has since jumped up, and by the following year she was already in Top 100 (senior). However, she still played in the junior circuit for the first half of 2002, and clinched two more girls' grand slam titles (Australian Open doubles with Gisela Dulko and French Open singles).
At the US Open 2002, she beat Anna Kournikova at the first round, 6–3 6–0, in only 44 minutes.
Unfortunately, injuries have affected her performance in 2004, and forced her to withdraw from tennis until 2006. Her comeback was not very successful, however, although she did manage to reach Top 100 for doubles.