Lee, competing in the men's under-68kg, was one of two South Koreans to reach the seminfinals at the World Taekwondo Federation World Taekwondo Championships at Taekwondowon's T1 Arena in Muju, 240 kilometers south of Seoul.
Kim Jan-di also made the final four in the women's under-67kg.
There is no bronze medal contest at these championships, where the two losers of the semifinals will each earn a bronze.
Host South Korea is currently leading the competition with two gold medals.
Lee, the top seed here and also No. 1 in the WTF rankings, won the world titles in the under-63kg category in 2011 and 2013, and will try to add a third in a new weight class this week. The semifinals and the final will take place Tuesday.
|Lee Dae-hoon (Yonhap)|
Lee opened his day by beating Lakchai Hauihongthong of Thailand 34-10 in the round of 64. Lee then took down Yerassyl Kaiyrbek of Kazakhstan 39-27, and beat Edival Pontes of Brazil 25-7 to reach the quarterfinals.
Iran's Abolfazi Yaghoubijouybari gave Lee all he could handle in the quarterfinals. The Iranian actually led 11-10 after the second of three two-minute rounds. But Yaghoubijouybari looked gassed in the final frame, as Lee picked up five unanswered points for the come-from-behind win.
In Tuesday's semifinals, Lee will face Vlaimir Dalakliev of Bulgaria.
In the women's competition, Kim beat Victoria Heredia of Mexico 17-6 in the round of 32, and then defeated Polina Khan of Russia 14-8 in the next round.
The South Korean then blanked Farida Azizova of Azerbaijan 7-0 to advance to the semifinals, where she will take on Nur Tatar of Turkey on Tuesday.
Tatar is the 2015 world silver medalist who also won an Olympic bronze in 2016 and silver in 2012.
This is Kim's second world championships. She lost in the round of 16 in 2013 in Puebla, Mexico. (Yonhap)