Byeong Hun An was forced to endure an attritional Moving Day to join fellow South Korean Tom Kim at the summit of the Genesis Championship.
The home favourite had birdied the most holes during the first two rounds and looked set to accelerate from the chasing pack when he picked up a shot at the first on a glorious Saturday at Jack Nicklaus Golf Club Korea.
However, the World Number 36 only picked up two more shots, alongside two bogeys, in his one under 71 to sit alongside Kim at 12 under par.
The pair are one shot ahead of Frenchman Antoine Rozner, who carded a seven under 65 to initially set the clubhouse target, Portugal's Ricardo Gouveia and Italian Francesco Laporta in Incheon.
"I struggled a little bit today," An said. "The last two rounds have been almost perfect. I didn't have many birdie chances out there and when I did, I would just miss it by a little bit.
"It was one of those days. It's golf. It's been great the last few days, it happens and hopefully better tomorrow.
"I don't think it can get any better. I said at the start of the week that I would love to play with Tom in the final group on Sunday and hopefully one of us can come out on top."
An made a fast start following a brilliant approach into the first green and rolled in an opening birdie to stretch his lead to three shots.
After six straight pars, An went over the back of the par-three eighth to card his first bogey, which saw his lead get trimmed to one.
A hat-trick of birdies from the 14th saw Rozner climb into the logjam behind An, with the Frenchman sitting alongside Rasmus Neergaard-Petersen, who was in the clubhouse, Gouveia, Laporta and Kim at ten under.
However, Rozner took advantage of the par-five last and when he rolled in his eighth birdie of the day from six feet, An had company in the lead at 11 under.
Kim was grinding it out with just one birdie on his front nine, but carded two more at the tenth and 12th.
He opted to take his medicine at the 14th after a poor tee-shot and it proved pivotal as he drained the monster 59-foot putt for the birdie which increased the leadership group to three.
However, An hit back at the same hole with a long birdie putt of his own to nudge in front at 12 under.
Kim dropped back after double bogeying the 15th but producing a stunning shot from the rough at the next to claw a shot back.
An blinked as he three-putted at the 16th to return to 11 under alongside Rozner at the summit, but compatriot Kim delighted the home fans with one of the shots of the day at the last to make his move.
The World Number 25 was rewarded for his risky approach by landing within four feet and when he holed the eagle putt, he was the outright leader.
An narrowly missed a birdie putt at the 17th but almost eagled the last himself when his chip rolled up just short, which he tapped in to ensure there was a Korean duo at the top.
"It felt great. Just to finish off the way I finished after that bad break on 15 just makes dinner taste so much better," Kim said.
"Obviously I've made a few mistakes this week, but those little things are coming together to back up those mistakes.
"What happened on 15, you can't control it, you know, one bad swing. You are really unlucky, hit the cart path and it's out of bounds. I had no idea!
"I told myself going up to that next tee that I'm making sure I'm birdieing a few holes coming in."
Rozner rolled in eight birdies and a bogey to catapult himself into contention, with Laporta recording a roller coaster round of seven gains, three dropped shots and a double bogey.
Gouveia, who started the week in 154th place, moved up to provisional 107th in the Race to Dubai Rankings in Partnership with Rolex after carding a three-under 69 to boost his chances of earning his playing rights for next season.
Denmark's Rasmus Neergaard-Petersen, Japan's Rikuya Hoshino and Spaniard Alejandro Del Rey are at ten under.
South African Brandon Stone, New Zealand's Daniel Hillier and first round leader Ivan Cantero are one shot further back.
