Byeong Hun An holds a one-shot lead over Scotland's Martin Laird going into the final round of the Waste Management Open in Phoenix.
Both players shot six-under-par rounds of 65 at TPC Scottsdale's Stadium Course, with halfway joint-leader An claiming an outright advantage on 16 under par.
The Korean, who shot to prominence when he won the European Tour's flagship BMW PGA Championship at Wentworth in 2015, took advantage of some excellent approach play on the front nine to make four close-range birdies.
Further gains came from 12 feet on the 10th and six feet on the 17th to give An a slender advantage over Laird, who after dropping a shot on the second responded with four consecutive birdies from the third.
The 34-year-old, who picked up the last of his previous three PGA Tour titles in Texas four years ago, then picked up further shots on the 13th, 14th and 18th.
"I played really nicely today," Laird, who moved to America as a 17-year-old and resides in Arizona, told pgatour.com. "Yesterday was a little bit of a struggle with my iron game but I got that sorted out after I played and today I played really nicely.
"I was right in the mix in 2015, I like this golf course, I'm comfortable here. I live five minutes down the road.
"I know that if I can go out and play like I did the last three days I'll be right there tomorrow."
Defending champion Hideki Matsuyama, Canada's Graham DeLaet and American pair Michael Kim and John Peterson share third on 12 under.
Brendan Steele, who shared the halfway lead with An, could only manage a one-under 70 to slip into a share of seventh.