(Reuters) - Kim Si-woo completed a brilliant weekend for South Korean golf when he blew away the field for a five-stroke victory at the Wyndham Championship in North Carolina on Sunday.

Eleven years after his compatriot K.J. Choi won in Greensboro, Kim added his name to the Sam Snead Cup, matching the lowest numerical score posted in the event that dates back to 1938.

Barely 24 hours after Park In-bee captured the Olympic women's golf gold, Kim carded 67 to finish at 21-under-par 259, capping off his performance with a 13-foot birdie at the final hole at Sedgefield Country Club.

An hour-plus rain delay with two holes left merely postponed the celebrations.

Englishman Luke Donald (67) put his mediocre recent play behind him to take second place on 16-under, but the day belonged to Kim.

The 21-year-old South Korean, in his 38th start on the PGA Tour, is the youngest winner since Jordan Spieth won the 2013 John Deere Classic at the age of 19 years, 11 months.

And Kim is the fifth South Korean champion on tour, joining Choi (eight wins), Yang Yong-eun (two), Bae Sang-moon (two) and Noh Seung-yul (one).

Kim used his textbook-perfect swing to card a course record second-round 60 and never looked back, knocking approach shots close to the hole to distance himself from the field with precise shotmaking rather than a hot putter.

He was so far ahead with nine holes left that the result was hardly in doubt, even after he made three bogeys in five holes from the 10th.

"I aggressively played. I already made top 125 (in tour rankings), feel confidence so I don't have any fear to attacking the pin," he told reporters about having already retained his tour card and qualified for the FedExCup.

"I never expect any course record. I'm very happy being the youngest winner this year."

Despite his tender age, Kim is not the youngest ever champion in Greensboro. That honor belongs to the late Seve Ballesteros, who was 20 when he won in 1978.

Ballesteros went on to win the British Open three months later, the first of five major championships for the Spaniard.

Kim's immediate ambitions are not quite so grandiose.

"My goal is winning one more time next two years," he said, perhaps being overly modest.

(Reporting by Andrew Both in Cary, North Carolina; Editing by Larry Fine)