Dustin Johnson surged into the lead at the WGC-HSBC Champions on Friday with a sizzling 63, but Brooks Koepka remains firmly in contention after a late charge.
Johnson was four behind overnight leader Koepka but turned on the style on the back nine with seven birdies, having picked up two shots before the turn.
Big hitting off the tee enabled Johnson to rack up the birdies and, with momentum on his side, he soon surged to the top of the leaderboard as he came home in 29.
The world number one's 63 was just one shot short of Martin Kaymer's course record and leaves him in contention to become the first player to win three of the four World Golf Championships in a single season.
"Obviously I played very well today but I actually got a putter like about 20 minutes before I teed off, it's a Spider, so it's one that I've used before," said Johnson, who won this tournament in 2013.
"I wasn't really pleased with the one I played with yesterday so the guys here in China made me one. I got it right before I walked to the tee. I hit a few putts on the practice green with it and I was like, 'oh, this will work pretty well'. Went out and holed a lot of putts today, so I kind of like it.
"It's a golf course that I enjoy playing. It suits my eye very well.
"You've got to drive it well. For me, if I drive it good out here, I feel like I can make a lot of birdies. The par fives, I can reach all the par fives if I drive it in the fairway.
"The rest of the holes, I feel like if I'm in the fairway I can attack the golf course."
Koepka made a solid start with birdies at his opening two holes, but pars became the order of the day as Johnson moved into view.
As Johnson pushed clear it looked as though his close friend would be left in his wake, but Koepka finished with a flourish to end the day just one shot behind.
"We're not going to take things too seriously. We like to relax. We like to work out."-- PGA TOUR (@PGATOUR) October 27, 2017
Brooks & DJ: One of golf's best friendships. pic.twitter.com/wYneB2ELzR
The reigning U.S. Open champion picked up two shots in his final three holes to sign for a 68, leaving him 12 under heading into the weekend.
Justin Rose and Kiradech Aphibarnrat sit on nine under, while Patrick Reed completes the top five a further shot behind the duo after his 70.
Meanwhile, Hideki Matsuyama's miserable title defence showed no signs of improving after he carded a second successive 74, leaving him four over and 17 shots off the lead.