Sung's Olympic debut came as a seventeen-year-old teen at the
2000 Summer Olympics in
Sydney. There, he posted a lifetime best of 57.12 to lead the second heat of
men's 100 m backstroke by exactly one second ahead of Uruguay's
Diego Gallo, but finished only in thirty-first place from the prelims. Two years later, Sung won two bronze medals, as a member of the South Korean swimming team, in the men's 400 m freestyle and medley relay at the
2002 Asian Games in
Busan, with a total time of 3:23.58 and 3:46.44, respectively. At the
2005 Summer Universiade in
İzmir, Turkey, Sung defeated Japan's Masafumi Yamaguchi and United States'
Matt Grevers to earn a silver medal by two hundredths of a second (0.02) in the 50 m backstroke, posting a lifetime best of 25.59. The following year, he snared the bronze medal in the same event at the
2006 Asian Games in
Doha, Qatar, lowering his time at 25.57 seconds. Eight years after competing in his first Olympics, Sung qualified for his third South Korean team, as a 25-year-old, at the
2008 Summer Olympics in
Beijing. He broke a new South Korean record on a bodysuit and cleared a FINA B-cut time of 55.43 (100 m backstroke) from the Good Luck Beijing China Open. In the
100 m backstroke, Sung challenged seven other swimmers on the third heat, including five-time Olympian
Derya Büyükuncu of Turkey. He finished ahead of France's
Benjamin Stasiulis in fourth place by a nine hundredth (0.09) margin, lowering his Olympic time to 54.99 seconds. Sung failed to advance into the semifinals, as he placed twenty-third out of 45 swimmers in the evening preliminaries. ==Personal life==