Si Woo Kim narrowly misses out on magical 59 but surges clear at Byron Nelson

Kim looked set to join the exclusive club of players to shoot a sub-60 round on the PGA Tour after draining his 12th birdie of the day at the 17th.

But his bid for history slipped away at the par-four 18th. With adrenaline clearly flowing, Kim's approach sailed beyond the green and he was unable to save par after leaving himself an 18-foot putt following his chip shot. The closing bogey left him with a remarkable 60 and a tournament total of 18-under 240.

Kim nevertheless opened up a sizeable advantage over a chasing group that included defending champion Scottie Scheffler, fellow South Korean Im Sung-jae, Japanese rookie Kensei Hirata and former US Open winner Wyndham Clark.

Im produced one of the rounds of the day with a dazzling 10-under 61 that featured a hole-in-one and a closing eagle, while Scheffler and Clark both carded eight-under 63s. Hirata remained firmly in contention after signing 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.

"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."

Earlier, World No 1 Scheffler picked up five shots in the space of four holes with a series of three birdies and an eagle.

"Sometimes you feel like you're playing badly when you're watching somebody just hit it to eight feet and make it on every hole," he said.