Li Haotong posted a flawless 65 on the second morning of the 2020 US PGA Championship to climb to the top of the leaderboard, while Tommy Fleetwood was not far behind after shooting the joint lowest round of the tournament so far.
Li only found four fairways on Friday morning but produced some stunning approach play and putted well to make five birdies and no bogeys and move to eight under par.
China's Li, who finished third in the 2017 Open Championship after a closing 63 at Royal Birkdale, was three shots clear of the chasing pack as he walked off the 18th green but saw his advantage cut to two shots by fellow early starter Fleetwood after he signed for a second round 64.
Li is used to battling it out with some of the world's finest golfers, having held off Rory McIlroy to win the 2018 Omega Dubai Desert Classic - the second of his two European Tour titles.
And he showed how comfortable he is on the biggest stages on day two at TPC Harding Park as he got off to an excellent start.
Beginning the day two shots behind overnight co-leaders Jason Day and Brendon Todd after posting an opening 67, it took him just two holes of his second round to pull level.
After sending his approach to three feet at the first, he tapped in for an opening birdie before holing from 22 feet on the second green to join Day and Todd at the summit.
The 25-year-old grabbed the outright lead after draining another lengthy birdie effort at the fifth before extending his advantage to two shots with his fourth birdie of the day on the ninth.
Li, who struggled in his two events since the coronavirus hiatus before this week, then picked up another shot at the par five tenth to get to eight under and extend his lead to three.
Todd briefly closed the gap to two shots with a birdie at the long fourth but he then bogeyed the sixth to fall back to five under.
Li confidently knocked in his testing par putt from five feet at the 15th before narrowly missing birdie chances on the 16th, 17th and 18th as he parred his way home.
After his round, Li said he expects his experience at The Open three years ago to help him over the weekend in San Francisco but insisted he is only thinking about playing his best golf rather than where he finishes.
He said: "It (Birkdale) was a long time ago. It's definitely good to have that experience in my mind, and definitely it will help to play the next two rounds.
"I've still got two rounds left. Long way to go. Just want to play my best. If it happens, it happens."
Starting from the tenth tee, World Number 13 Fleetwood covered the back nine in 31 with four birdies and picked up another shot on the first courtesy of a magnificent approach to eight feet.
He dropped his first shot of the day on the second but bounced back with a birdie on the fourth before getting to six under with another gain at the seventh.
Fleetwood, who finished runner-up to Shane Lowry in last year’s Open, could have closed the gap on Li to a single shot at the ninth - his last - but his 23 foot birdie putt missed the cup.
He said: "Today felt good. I felt like I worked my way into the round well and then gained momentum and then kept it going."
Paul Casey was a single shot behind his countryman Fleetwood in the big group on five under alongside Americans Cameron Champ - who shot the day's other 64 - and Todd, as well as afternoon starter Day.
Casey started from the tenth and made birdies at his first and third holes before picking up another birdie at the start of his back nine to sign for a flawless 67 and banish the memory of yesterday's closing double bogey.
