Kim earned his maiden win in spectacular fashion as he led the tournament since posting a course-record 60 in the second round.
He closed with a three-under 67 to run away with the title by five strokes over second place finisher Luke Donald.
"He looked like he was very much in control of his game and he was going to be a hard man to catch," Donald said of Kim.
Kim finished four rounds at the Sedgefield Country Club course at 21 under for the 21-year-old.
Kim became the youngest international winner on US Tour since Seve Ballesteros of Spain won in 1978. Of all the places, Greensboro, North Carolina was also the sight of Ballesteros' early career celebration.
With a storm approaching as Kim went to the 17th tee, play was suspended for one hour and 21 minutes. He led Donald by four shots at the time, with six golfers still on the course.
Kim built a seven-shot lead while on the front side before hitting a rough patch.
Kim made bogey on No 10 as rain moved in. But he held a five-stroke lead over Kevin Na and Brandt Snedeker at the time.
After Kim made three bogeys on the first five holes of the back nine, Jim Furyk was within four shots.
Then a two-putt birdie on the par-five 15th seemed to steady Kim, who began the day with a four-shot advantage. Kim also birdied the last hole.
Hideki Matsuyama (67) and Snedeker (67) tied for third.
"You had to play a perfect round of golf. If he did what he has been doing all week he's really really tough to catch," Snedeker said of Kim.
Furyk's double-bogey six on the last hole left him with a 70 and a tie for 10th eight shots adrift of Kim.
