Former Masters runner-up Rickie Fowler claimed a two-stroke lead at the CJ Cup as Keith Mitchell surrendered his five-shot advantage on the third day in Nevada on Saturday.
Fowler carded a nine-under-par 63 to be 21 under after three rounds and two shots clear of four-time major champion Rory McIlroy at the Summit Club.
The 32-year-old American made his move on the front nine, with five birdies in six holes, finishing with a bogey-free round.
It marked Fowler's best round in three years, and it was only the third time in his career he had hit all 18 greens in a round.
"I haven't been there a lot the last couple of years, so it's nice to be back in that position," Fowler told reporters. "It's been a long time coming. It's been a long road, tough times. We're not done."
McIlroy represents his main competition ahead of the final day, after an exceptional penultimate round with a 10-under-par 62.
The Northern Irishman reeled off five consecutive birdies on the front nine before finishing his round with an eagle after a fine approach and 21-foot putt on the 18th hole.
McIlroy is 19-under 197 after three rounds, ahead of Mexico's Abraham Ancer, USA's Robert Streb and Australia's Adam Scott by one shot.
Mitchell slipped back to 17-under alongside Tyrrell Hatton, giving up his five-shot lead at the halfway point with a disappointing day.
The one-time PGA Tour champion had dazzled with rounds of 62 and 64 on the opening two days but came back to earth with a one-over-par 73, which included two bogeys and two double bogeys. Mitchell sunk a 28-foot putt for birdie on the 18th hole to lift his spirits.
Former world number one Jordan Spieth had been among the pack behind Mitchell after two rounds but he had also struggled with an even-par 72 third round.
Spieth is eight strokes behind leader Fowler, following a frustrating round that included one birdie and one bogey.
This year's Open Championship winner Collin Morikawa is 14 under, while former major champions Sergio Garcia (12 under), Brooks Koepka (11 under), Justin Thomas (10 under) and Dustin Johnson (nine under) are well off the pace.