Jeff Overton was third at 14 under after a 68.
Jason Bohn had a 69 to reach 13 under, and Sean O'Hair shot a 63 to join first-round leader J.J. Henry, defending champion Ryan Moore, William McGirt, Ryo Ishikawa and Russell Knox at 12 under.
Sweden's Anna Nordqvist shot a 2-under 70 to remain tied for the lead with Australia's Katherine Hull-Kirk after the second round of the KEB HanaBank Championship at Incheon, South Korea.
Nordqvist had four birdies and two bogeys to move to 7-under 137, while Hull-Kirk had an eventful day with an eagle, a double bogey, five birdies and three bogeys in her 70.
Bernhard Langer overcame a bad start to take a two-stroke lead after the second round of the Champions Tour's Greater Hickory Classic at Conover, N.C.
Second behind Kenny Perry in the Charles Schwab Cup standings, Langer bogeyed the first two holes on the reconfigured Rock Barn layout, then made six birdies for a 4-under 66.
Webb Simpson -19
Chesson Hadley -15
Jeff Overton -14
Jason Bohn -13
D. Summerhays -11