He shares second with Sweden's Alex Noren and Daniel Gavins of England and it will be a welcoming return to contention for Fox who has overcome a recent knee injury and an airline losing his golf clubs in recent weeks.
Of notable names further back, Rory McIlroy, Billy Horschel and Padraig Harrington are all four shots back from Fox at seven-under.
Ko shrugged off a double bogey to four birdies on the back nine to card a four-under 67 in the third round at The Ascendant LPGA.
Ko had six birdies across her round to move to 10-under, one shot behind co-leaders Xiyu Lin on China and England's Charley Hull. A top three finish would see Ko move to the top of the Race to the CME globe standings.
Her only blip on the round was a double bogey five on the par three 10th, but she responded with four birdies over the next six holes to jump back up the leaderboard.
In the Challenge Tour, Hillier is still a chance for back-to-back victories but has lost his lead heading into the final round at the Hopps Open de Provence event in France.
Hillier, who won the Swiss Challenge tournament last week, sits in a share of second following a third round 70. He is two shots back from leader Joel Sjoholm of Sweden. A strong finish should all but book Hillier a place on the DP World Tour next year.
The 24-year-old was 26th in the Tour standings two weeks ago and was sitting 13th after his win last week. As it stands, a second placing in Mallemort would see him jump to third.
The top 20 players after the season-ending Tour finale in Spain in November secure their main Tour cards.
