LOS ANGELES (AFP) - South Korea's Kim Si Woo extended his lead to four strokes at the PGA Tour's Wyndham Championship by shooting a six-under 64 in the third round on Saturday.

The 21-year-old was not as dominant as a day earlier, when he fired a course-record 60, but he managed to stay at the front of the pack for all of Saturday's round at the Sedgefield Country Club course in Greensboro, North Carolina.

Kim rolled in a birdie on No. 18 to reach 18-under 192 after 54 holes.

"My first time in the final group," Kim said. "I am trying to win.

"I think tomorrow there is much pressure, but I'm just trying to putt well and keep my confidence."

First-round co-leader Rafa Cabrera Bello, of Spain, moved up to second place with a 65, while American Jim Furyk (67), Kevin Na (67) and Luke Donald (64) are five shots back in a tie for third.

Plenty of eyes will be on Furyk on Sunday because two weeks ago he posted a 58 for the lowest round in USPGA Tour history in the last round of the Travelers Championship.

Greensboro fans have been yelling "58" at Furyk all week.

"It's not driving me crazy," he said. "It happened and in my mind, when I'm out there playing in a tournament, it happened and it's over with."

Furyk eagled the par-five 15th hole to move to 14-under and followed that with a birdie on the next hole, but he had bogeys on the last two holes.

Na posted five straight birdies through No. 10 to pull even at 15-under, but Kim responded with birdies on Nos. 13 and 15.

Donald had his best round of the tournament to move up the leaderboard.

Former tournament winner Brandt Snedeker finished at 65 and was six shots back in a tie for sixth with Billy Horschel (64), Hideki Matsuyama (68) of Japan and Graeme McDowell (64) of Northern Ireland.

Another former champion Patrick Reed (2013) is the tournament's most-recent winner still in the field.