The forward snapped-up from Bundesliga side Bayer Leverkusen last week made it 14 goals in 45 internationals in the second phase of Asian qualifying for Russia 2018.
'Sonny' finished well from 12 yards to make it 2-0 after 12 minutes, smashed home his second from a tight angle for 4-0 in 74 minutes and completed his hat-trick with a curler from the edge of the box for 7-0 in Hwaseong.
The victory sees South Korea top Group G. There are eight groups in the second phase of Asia qualifying - including the likes of Australia, Japan, Iraq, Iran and North Korea - with the group winners and four best second-placed teams going through to the final qualifying stage. The final stage consists of two groups of six with the two group winners and runners-up progressing direct to Russia. The two third-placed teams go into a final play-off.
Sonny and South Korea next face Lebanon in Beirut on Tuesday (September 8).