Danny Lee fired an 8-under 63 on Saturday to jump four strokes clear of the field after three rounds of the Rex Hospital Open.
Lee, who will go for his second tour victory on Sunday, finished 54 holes at 17-under-par 196.
Andrew Putnam carded a 66 and Edward Loar posted a 67 as they both moved into second place at minus-13.
Michael Putnam, Andrew's older brother, fired a 6-under 65 to move into a share of fourth at 12-under-par 201. He was joined there by second-round leader Chesson Hadley, who managed a 2-under 69 in round three.
Josh Broadaway is alone in sixth place at minus-11 after a 6-under 65 on Saturday at TPC Wakefield Plantation.
Lee trailed by one at the start of the round, but was in control by the time he hit the back nine. He posted birdies at the third and fifth to move to minus-11.
The 2011 WNB Golf Classic winner poured in three consecutive birdie chances from the eighth to jump into the lead at 14-under.
Lee, the 2008 U.S. Amateur champion, notched back-to-back birdies at 12 and 13 to extend his lead. After four pars in a row, Lee birdied the last to push his lead to four after three rounds.
"I thought everybody was playing good so I was just focusing on each shot and trying to make as many birdies as possible. I shot 8-under, what could go wrong?" Lee asked. "I don't want to think ahead right now. This is only the third round. I just want to play another round of golf and see what happens."
Andrew Putnam picked up three birdies on the front nine to make the turn at 11-under. After five pars in a row, he posted back-to-back birdies at 15 and 16 to post 13-under.
Loar birdied the third, fifth and seventh en route to making the turn at minus-12. He birdied the 10th, but stumbled to bogeys at 14 and 15 to slip to 11-under. Loar birdied the final two holes to gain a share of second.
NOTES: Lee holds the 54-hole lead for the second time in his Web.com Tour career. The first time came in his title defense at the WNB Golf Classic, where he closed with a 72 and finished in second ... Jim Renner had a hole-in- one on the 12th for the second ace of the week.