The 14-year-old Thompson, from Coral Springs, Fla., is trying to become the second-youngest winner in LPGA Tour history _ and the youngest in a full event.
Marlene Hagge won the 1952 Sarasota Open 14 days after her 18th birthday and took the Bakersfield Open two months later, but both were 18-hole events. Paula Creamer won the 2005 Sybase Classic at 18 years, 9 months to become the youngest winner of a full tournament.
Thompson, the sister of PGA Tour player Nicholas Thompson, won the 2008 U.S. Girls' Junior and tied for 34th in July in the U.S. Women's Open. She shot a 65 on Thursday.
Ochoa (68), Laura Davies (65), Yani Tseng (63) and Giulia Sergas (65) matched Thompson at 10-under 134 on The Senator course at the Robert Trent Jones Golf Trail's Capitol Hill complex. Tseng matched the tournament record with her 63.
Sophie Gustafson, the winner last week in California, was 9 under after a 65, and Michelle Wie (70) and first-round leader Janice Moodie (72) topped a group at 8 under.