The CJ Cup Byron Nelson: Jordan Spieth's birdie blitz not enough as Si Woo Kim leads and Scottie Scheffler keeps pace

Jordan Spieth fired nine birdies to reach 12‑under par at The CJ Cup Byron Nelson, while Scottie Scheffler enjoyed a strong second round too, but both trail runway leader Si Woo Kim after two rounds.

Kim shot a stunning round of 60 to move to 18 under for the tournament so far, five clear of Scheffler and the chasing pack.

The South Korean hit 12 birdies in a remarkable second-day showing, and finished with a bogey at the 18th.

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Three-time major winner Spieth started his back nine - the front side of TPC Craig Ranch - with six consecutive birdies on the way to a nine-under 62 in the second round on Friday.

Scheffler started at five under in an afternoon pairing with Brooks Koepka, who opened with a 63 and is looking for his first victory since his return to the PGA Tour from LIV Golf.

While Scheffler shot a round of 63, Koepka shot a round of 69 to sit back on 10 under.

Spieth credited a crucial par save at the 18th for setting up his birdie binge, which started with a 12-footer. He hit the first four fairways after struggling off the tee on his first nine, made a 12-footer at the fourth, a four-footer on the fifth and capped the surge from nine feet on the sixth.

After Spieth put his tee shot 29 feet right of a pin to the far left at the seventh, his playing partner Sungjae Im bounced his 222-yard shot between the fringe and the hole and watched it roll in. The 28-year-old was tied for the lead at that point.

"That was one of the prettiest hole-in-ones I've ever seen," Spieth said. "Prettier than any one I ever made. There's only a few people that would land that left of it on purpose. He might be one of them."

Spieth's birdie run ended when his 29-footer at the seventh came up about a foot short, while Im added another eagle with a 14-foot putt at the ninth.

Spieth finished a bogey-free round with a birdie on the ninth hole. Im had a bogey and seven birdies to go along with his hole-in-one and eagle.

"I was hurting my head trying to figure out what our best ball was," Spieth said. "I think it was 57, which is pretty good."

Spieth, who contended on Sunday as a 16-year-old high schooler at his first Nelson in 2010, finished fourth a year ago when Scheffler won by eight at 31 under while tying the tour's 72-hole scoring record of 253.

The 32-year-old Spieth with 13 tour victories was actually worried about the cutline when he was five under at the turn. Then he went on to match his career best at the Nelson from the final round last year.

"Just a lot of it just comes down to knocking in putts," he said. "It's not a normal week, and it's fantastic. Now that our families have grown and stuff, you get the little kids coming out, and it makes it even better."

Watch the The CJ Cup Byron Nelson live until Sunday on Sky Sports Golf, where Scottie Scheffler is the defending champion. Get Sky Sports or stream with no contract.