By Andrew Both

GREENSBORO, North Carolina (Reuters) - South Korean Kim Si-woo was focused intensely on his own task, birdying the final hole as he turned a narrow advantage into a four-shot lead after the third round at the Wyndham Championship on Saturday.

Kim was almost flawless, carding a six-under-par 64 to move within sight of his first PGA Tour victory.

It was a grand day for South Korean golf as compatriot Park In-bee won Olympic golf gold earlier in the day, but Kim did not draw inspiration from Park's achievement.

Indeed, the single-minded Kim was not even aware of the final round in Rio.

"Finished Saturday?" he asked, before reacting to Park's victory, "that's great."

Kim, who began the day with a two-shot cushion after a second-round 60, birdied the first two holes and hardly put a foot wrong at the Sedgefield course.

The 21-year-old from Seoul put an exclamation mark on his day by stiffing his approach shot to three feet for a birdie at the last as he posted an 18-under 192 total.

Spaniard Rafa Cabrera-Bello shot 65 to jump into second place on 14-under, a shot ahead of Americans Jim Furyk and Kevin Na and Briton Luke Donald on 13-under.

Na shared the lead after 11 holes and was two strokes behind going to the last, only to finish with a double bogey to plunge from second place. He did not stay for a chat with the media.

Kim was in a happier mood.

"I feel very good now. My shots much more consistent," he said, before adding that the only problem he faced was the pressure of leading.

Kim, a four-time Korean junior champion, cannot plan his victory speech just yet, with so many quality players within striking distance.

Cabrera-Bello, coming off a tie for fifth at the Olympics last week, continued his strong form and oozed confidence about his chances of a strong finish.

"There is damage to be done," he said of the Donald Ross-designed course, which is short by modern standards, and virtually defenceless when the greens are soft, as they were on Saturday.

"The greens are brilliant. Give yourself chances and you will roll putts and that's what I'm going to try to do tomorrow."

And 'Mr 58' Furyk cannot be discounted, despite bogeying the final two holes.

"I got off to a slow start and stayed real patient today. I was proud of that," said Furyk, who sank a 60-foot monster putt to eagle the par-five 15th.

Furyk shot 58, the lowest score ever on the PGA Tour, in the final round of the Travelers two weeks ago.

(Editing by Larry Fine)