 In 2006, Jang made his professional debut with Daegu FC, and finished as the top scorer in the Korean FA Cup that year.In 2008, Jang Nam-Seok, together with Lee Keun-Ho and Eninho, played a key role in the offense orientated tactics that was employed by Daegu FC that season.On 6 June 2008, he scored a goal within 40 seconds of kickoff in a home match against Ulsan Hyundai Horang-i.