Koch and Lu both fired a 5-under 67 at the Reunion Resort & Club, but Ochoa was again in position to add to her current stretch of sensational golf.
Ochoa has won her last three LPGA Tour events, including the year's first major championship. Her victory last week qualified her for induction into the LPGA Hall of Fame and the World Golf Hall of Fame.
"Of course I like my position right now," Ochoa said. "I'm still a little bit tired. I'm in position and I'm going to make sure I give myself a good chance to win the tournament on Sunday."
Veteran Juli Inkster was in a large group at 3-under 69 while defending champion Brittany Lincicome shot 74.