Unlike most South Korean badminton players Sung has focused on singles and in December 2011 she received a career high ranking of number seven in the world in that discipline.

Sung won her first Super Series Premier title early in 2013 at her hometown, at the Korea Open.

Sung reached the semi-finals at the All England, losing to eventual winner Tine Baun in a match that lasted for 76 minutes, with a final score of 22–24, 21–19, 19–21.

In 2013 Korea Open Grand Prix Gold, she went up against compatriot Bae Youn-joo and she was beaten in 3 sets, 21–19, 15–21, 21–9.

At the 2014 German Open Grand Prix Gold, she reached the final which Sayaka Takahashi won, 21–17, 8–21, 21–12.

At the 2014 Badminton Asia Championships, she became the first South Korean in 10 years to win the title, beating 1st seeded Wang Shixian 21–19, 21–15.

Women's singles Record against year-end Finals finalists, World Championships semifinalists, and Olympic quarterfinalists.