Started hitting golf balls at the beach near his house when he was 7. His father, Gu-huieun, has provided the guidance by caddieing for him in the early part of his career. Enjoyed a strong amateur career where he won the 2005 Korean Amateur Championship and 2005 Korean Junior Amateur. Was part of the Korean national team in 2006 and 2007. In 2006, finished tied for third at the Maekyung Open while he was still an amateur and followed that up with another top-10 at the Korean Open.
Achieved remarkable success in his rookie season on the Asian Tour when, at 17, he won his first title with victory in the 2008 Midea China Classic. Made an immediate impact after getting his Asian Tour card through the Qualifying School when, in addition to winning his first title, he claimed three runners-up finishes and an additional six to finishes-10s in 16 events.
Showed his immense talent by putting together seven top-10 finishes in 2009, with his best finish being a tie for fifth at the Worldwide Holdings Selangor Masters.
Won the European Tour's Maybank Malaysian Open in March 2010, defeating fellow Korean K.J. Choi with a stunning birdie on the final hole. Also placed fourth at the 2010 Omega European Masters. The win made him the second-youngest winner (18 years, 282 days) ever on the European Tour after Danny Lee (18 years, 213 days). Ended his 2010 European Tour season 34th in the Race to Dubai with €869,921. Was first on the Asian Tour order of merit which got him a spot in the 2011 Open Championship.