Louis Oosthuizen shot a blistering 9-under 63 on Friday to set a new 36-hole World Golf Championship record and open up a commanding five-stroke lead after the second round of the HSBC Champions at Mission Hills.
The 2010 British Open champion, the co-leader overnight, had eight birdies and an eagle to offset one bogey.
He now sits at 16-under 128 overall; the best 36-hole round score in the history of the World Golf Championship, bettering the 15-under marks set by Tiger Woods at the 2000 Bridgestone Invitational and the 2006 Cadillac Championship.
Reigning British Open champion Ernie Els jumped from 19th place after the opening round into a share of second with Australian Adam Scott.
Els made seven birdies on the front nine to card a 29-the lowest nine-hole score of the day. He finished the round with a 63.
Shane Lowry and Jason Dufner were in fourth place, six strokes behind the leader at 10 under. Phil Mickelson double-bogeyed his final hole to fall into a share of sixth with Dustin Johnson after moving into contention with two eagles on the front nine.
Oosthuizen again made the most of the five par-5 holes on the Olazabal Course at Mission Hills, birdying four and making eagle on the 566-yard seventh. He birdied all five par-5s in the first round on Thursday.
The South African nearly had a second eagle on Friday, too. After hitting his second shot into a bunker on the par-5 ninth, he hit a difficult chip shot over a ridge and onto the green that rolled 15 feet and missed the pin by inches.
Oosthuizen is having one of his best years on tour, with two titles and a runner-up finish to Bubba Watson after a play-off at The Masters. He says the highlight was a single shot - an albatross, or double eagle, which he hit on the par-5 second hole in the final round at Augusta.
He's not expecting to repeat the feat at Mission Hills, but he is hoping he can keep hitting well off the tee on the long holes to bag as many birdies as he can.
Mickelson, a two-time HSBC Champions winner, played a superb front nine with two eagles and two birdies to move into a share of second place with Scott at the turn.
But on the 18th he barely cleared the lake and landed in the rough on a steep slope next to the green. Balanced awkwardly with one foot on a rock and the other on the hill, he missed the ball completely with his first swing. He popped it onto the green with his second attempt but then missed a 10-foot putt for bogey.
Scott, the co-leader with Oosthuizen after the first round, made four birdies to keep pace on the front nine before blundering an opportunity for birdie on the par-5 ninth, which he had eagled the day before.
After positioning himself well with a deep second drive that nearly reached the green, the Australian left his chip shot short, setting up a difficult 10-foot putt which he missed, taking par.
Scott's struggles continued on the back nine with three bogeys to go along with his three birdies.