SOUTH KOREA, 13 Sept 2015, (AFP) - The 24-year-old started the day with a two-stroke lead at the top of the leader-board and never looked like relinquishing his position, making an eagle at the fifth and then birdying holes seven, eight and nine.
"I am proud of the way I handled the pressure. Four shots is a nice margin but it was all much closer than that," Lee said.
Compatriot Kim Meen-Whee also carded a 66 to move up into second position four shots behind Lee.
Two other Koreans, Wang Jeung-Hun and Lee Dong-Min, tied for third place three shots back.
"It is an incredible feeling," Lee said of his victory -- only his second as a professional.
"I have been playing well recently and could not have found a better time to find my form. The Korea Open is our biggest event and it is a great honour to win," Lee said.
Australian Steven Jeffress, the first and second round leader, and Korean Moon Kyong-Jun finished equal fifth after rounds of 72 and 69 respectively.
Korean star Kim Kyung-Tae, one of the pre-tournament favourites after his victory in last weekend's Fujisankei Classic, returned a 71 to end up tied in 14th place.
Kim Meen-Whee, a gold medal winner at the 2010 Asian Games, said he was happy with his runner-up spot.
"I will take a lot of confidence from this. Lee was always a bit too far ahead so finishing second here was a great result," the 23-year-old said.
Leading scores (South Korea unless stated):
271 - Lee Kyung-Hoon
275 - Kim Meen-Whee
278 - Wang Jeung-Hun, Lee Dong-Min
280 - Moon Kyong-Jun, Steve Jeffress (AUS)
281 - Lee Ji-Hoon, Kim Seng-Yong, Park Jae-Bum
282 - Park Sang-Hyun