On June 25, 1950, Lee subsequently led his division to the capture of Seoul in the First Battle of Seoul. He was awarded his decorations for this action. After Seoul, Lee was leading his division south when it encountered forces of Task Force Smith at Osan, defeating the US Army in its first engagement in Korea, the Battle of Osan on July 5. Lee's division went on to fight the US forces back further at the Battle of Pyongtaek, Battle of Chonan, the Battle of Chochiwon and the Battle of Uijeongbu. At the Battle of Taejon from July 12–20, Lee's division was pivotal in routing and defeating the US 24th Infantry Division, a feat for which it was upgraded to the status of a guards unit. Lee also received the Hero of the Chosun Minjujui Inmun Kongwhakuk (Hero of the Democratic People's Republic of North Korea) and the Order of the National Flag, First Class for his accomplishments.