A group of six players is 5-under 67, and three others are 4-under 68.
Defending champion Jason Gore struggled to a 1-over 73 and is tied for 70th place.
LPGA teenager Michelle Wie, who has missed the cut in nine of the 10 men's events in which she has played, shot 5-over 77 to tie for 125th place.
"I feel like if I can make some putts tomorrow, I can really shoot a low score," said Wie, who has a 13-shot deficit. "It all feels good. I'm hitting my irons good. It didn't feel like I shot a 5-over today."