The 24-year-old is placed third heading into the final round.
The 24-year-old is tied for fourth place, after a strong second round.
In her last pre-Olympics hit-out, the Kiwi is just off the leading pair in France.
The 24-year-old began the day a stroke behind the leader.
The 2010 champion is in pole position for another crown, sitting at 12-under.
Fox is seven shots back of leader Oosthuizen, tied for 17th after his second round.
Elsewhere, fellow Kiwi Daniel Hillier is tied for 91st after a two-over first round.
"It makes it feel like home having a familiar face there to play with."
Danny Lee posted an X-Ray on his Instagram page.
"Now it's fair game," says the US golfing star.
"He came in so confident and we thought he was going to take a picture or something".
Daniel Hillier has secured one of the final spots in the event starting next month.
The Kiwi is tied for 29th after an even-par opening day at Johns Creek.
The Spanish golfer has bagged his first major title in a scintillating finish at Torrey Pines.
The Kiwi overtook American Nelly Korda in the race to the season-ending tournament in Florida.
The Kiwi recorded four birdies and two bogies to move just three shots off the lead.
The Kiwi shot a second-round two-under to move within five shots of the leader.
The Kiwi carded five birdies and five bogeys on her first day in California.
Spectators have been removed by security, after taunting DeChambeau during his rounds.
The Kiwi carded four bogies, one double bogey and the sole birdie, to fall to nine-over par.