Dong-hwan Lee fired an 8-under 64 on Saturday to grab a 2-stroke lead after four rounds of the PGA Tour Qualifying School.
Lee finished 72 holes at 19-under-par 269.
Meen Whee Kim, who led after the second and third rounds, stumbled to a double-bogey on the 18th to post 1-over 73. That dropped him into a share of second place at minus-17.
Kim was joined there by Edward Loar (71), Vaughn Taylor (70) and Richard H. Lee (64). Taylor is a 2-time winner of the Reno-Tahoe Open, while Lee fired a 64 to jump from a share of 31st into a tie for second.
Jin Park (69), Steve LeBrun (71), Kris Blanks (70) and Billy Horschel (71) shared sixth place at 16-under-par 272.
Heath Slocum, a 4-time PGA Tour winner, shot 70 and 2008 Canadian Open winner Chez Reavie carded a 67 and they are among seven players tied for 10th at 15- under 273.
The top 25 and ties at the end of the tournament will receive PGA Tour cards for 2013, while the next 50, plus ties, will earn Web.com Tour cards. Players are competing for three rounds each on the Stadium Course and the Nicklaus Tournament Course at PGA West.
Dong-hwan Lee started on the back nine of the Stadium Course and flew up the leaderboard with three straight birdies from the 11th. He birdied 16 and 18 to make the turn at minus-16.
The South Korean birdied the second, then parred his next four holes. Lee grabbed a share of the lead at 19-under with birdies at seven and nine.
Kim remained tied for the lead until the final hole, where he faltered to a double-bogey.
Robert Karlsson birdied the second and eighth to briefly grab the lead at minus-19. He stumbled to a double-bogey on the ninth, then played the back nine in 3-over par. Karlsson posted a 3-over 75 to slide into a share of 17th at 14-under 274, where he stands alongside Matt Jones and Nicholas Thompson, who both shot 68 on Saturday.
NOTES: This 6-round marathon goes until Monday ... Gary Christian withdrew during the round with a rib injury, while Marcus Fraser and Gonzalo Fernandez- Castano withdrew after the round ended on Saturday ... Ernst is one of 12 players that made it through all three stages of Q School.