Kim Si-woo carded a spectacular 60 marred only by an agonising bogey at the last to seize a five-shot lead on Friday at the PGA Tour CJ Cup Byron Nelson in Mckinney, Texas.,
South Korea's Kim was poised to post just the 16th sub-60 round in PGA Tour history after his 12th birdie of the day at 17 – where he rolled in a 17-foot putt from the fringe.
But with the adrenaline pumping, his second shot from the fairway at 18 flew the green and he was unable to get up and down for par, his chip leaving him an 18-foot putt.
His 11-under 60 at TPC Craig Ranch in suburban Dallas left him on 18-under 240, five clear of defending champion Scottie Scheffler, South Korean Im Sung-jae, Japanese rookie Kensei Hirata, former US Open champion Wyndham Clark and American Jackson Suber.
Im surged up the leaderboard with an impressive 10-under-par 61 that included a hole-in-one and a closing eagle. Suber also shot 61, closing with back-to-back birdies for his share of second.
Scheffler, playing alongside his good friend and fellow Dallas resident Kim, carded an eight-under 63 that was matched by Clark, and Hirata signed for a six-under 65.
"I hit it great and putted great, so everything was perfect, other than the last hole," Kim said. "I'll still take it."
Inspired by Im's early round, Kim launched what he called his greatest round with a six-foot birdie at the first, rolled in a 17-foot birdie from the fringe at the third, then birdied three in a row at five, six and seven, where he drained a 20-footer.
He birdied four straight from the ninth through the 12th – where he blasted out of a greenside bunker to six feet.
'TOO PUMPED'
Birdies at 14 and 15 put him at 11-under for the day, but he said he didn't seriously think about shooting 59 – 12-under on the par-71 layout – until narrowly missing a birdie putt at 16.
"And then I made that putt at 17 and I was excited," Kim said.
"Eighteen, I knew it was going to be hard. I tried still to be aggressive on the second shot ... maybe I was too pumped. But it was a good round."
It overshadowed a stellar effort from Scheffler, who picked up five shots in the space of four holes with birdies at 11, 13 and 14 sandwiched around a 46-foot eagle putt at the 12th.
"Sometimes you feel like you're playing bad when you're watching somebody just hit it to eight feet and make it on every hole," the world No 1 said.
Im's scintillating round also came in a red-hot pairing as playing partner Jordan Spieth fired nine birdies in a nine-under 62.
Im and Spieth teed off on 10 and Im had four birdies before his only bogey of the day at the 18th.
UNEXPECTED BUT EXCITING
He birdied the first, third and fourth holes before watching in apparent surprise as his five-iron off the tee at the par-three seventh bounced on the green and rolled in the cup.
"I was surprised, but I hit a really good shot," he said, calling the moment "a little unexpected but obviously very exciting."
Im, whose 2026 campaign got off to a delayed start after a January wrist injury added a 14-foot eagle at the par-five ninth.
Spieth's birdie outburst included six in a row to launch his final nine.
With a 12-under total of 130 former world No 1 Spieth was in a group of five players sharing sixth.
"It was really fun," Spieth said. "You're feeding off each other, right? There's a lot of good golf going on."