Kevin Na equalled his career-low round with a 10-under par 61 to take a two-stroke lead over fellow American Patrick Cantlay in the PGA Tour Shriners Hospitals For Children Open.
On a day when plenty of players were going low on TPC Summerlin in Las Vegas, Na produced another strong performance on the greens in following up his second-round 62.
His 22-under total of 191 was a 54-hole record for the tournament, a home fixture for the South Korean-born American who won the first of his three PGA Tour titles in this event in 2011.
"I feel comfortable, I feel confident," said Na, who had 10 birdies without a bogey.
Cantlay, who won at TPC Summerlin in 2017 and finished second last year, kept the pressure on with eight birdies in his first 16 holes.
He faltered at the par-three 17th, where he was unable to get up and down from a greenside bunker, but closed with a birdie at 18 to cap a 63 for 193.
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It was a further two strokes back to American Pat Perez, who had an eagle and seven birdies in a nine-under 62 for 195.
"I've still got to keep the pedal to the metal," Na said of the task awaiting on Sunday.
"There's a lot of low scores out here. Anybody could shoot eight- or nine-under."
"I had nothing," he said. "I hit it to about 25 feet and made a 25-footer that broke six feet for par."