Shenzhen - Louis Oosthuizen picked up six shots in just five holes on the way to a red-hot 63 and a big five-stroke lead in the $7 million WGC-HSBC Champions on Friday.
An eagle on the par-five seventh sparked a blazing run from the 2010 British Open winner, who birdied his next four along with 15 and 16 for a nine-under-par round and a total of 16-under 128 at southern China's par-72 Mission Hills.
Oosthuizen's round, blotted only by an early bogey on the second, opened up a healthy advantage over a top-quality chasing pack led by Adam Scott and Ernie Els, who were tied on 11 under par.
"You can see there's a lot of birdies out there with five par-fives," said Oosthuizen, who was greeted at the clubhouse by his wife and young daughters, who are travelling with him.
"But I'm making it easy for myself -- I'm hitting a lot of good shots. It's far from over, there's a lot of golf left. I need a good round tomorrow to get myself in position for Sunday."
Four-time Major-winner Els turned at seven under par and added two more birdies on his way back for a 63, matching his fellow South African Oosthuizen, while Scott shot 68.
Phil Mickelson, the event's only double winner, was set for a share of second place until he found greenside rocks on the 18th for double-bogey, dropping down to tied sixth with Dustin Johnson.
Jason Dufner, Mickelson and Johnson's American Ryder Cup team-mate, shot 66 to share fourth spot with Ireland's Shane Lowry, who had 68.
Scott, who had shared the first-round lead with Oosthuizen, played a sumptuous front nine studded with four birdies but he stumbled on his return with three bogeys and another three birdies.
"I played OK today -- I got off to a good start but on the back nine I missed a few greens and I had to scramble, and it's tough when it's fast around the greens," said Scott.
The Australian escaped from a bunker on the third hole for his first birdie of the day, and he picked up further shots on four and five to take a two-shot lead early in the round.
A inappropriate cry of "Adam, we love you!" from two female marshals spurred him on, but it was Oosthuizen who then took charge with his eagle on the par-five seventh, cueing up a birdie blitz around the turn.
Oosthuizen birdied the par-three eighth, escaped out of a bunker to within a foot on nine, drained a 20-footer on 10 and then chipped to an unmissable distance on 11.
Two more birdies on 15 and 16 completed a pleasing day's work for the 30-year-old, who now has great chance of recording his sixth win and the second biggest of his career, after the 2010 Open.
Leading second-round scores at the $7 million WGC-HSBC Champions on the Olazabal Course (par-72) at Mission Hills in southern China on Friday:
128 - Louis Oosthuizen (RSA) 65-63
133 - Adam Scott (AUS) 65-68, Ernie Els (RSA) 70-63
134 - Jason Dufner (USA) 68-66, Shane Lowry (IRL) 66-68
135 - Dustin Johnson (USA) 67-68, Phil Mickelson (USA) 66-69
136 - Luke Donald (ENG) 68-68, Scott Piercy (USA) 68-68, Bill Haas (USA) 69-67, Thorbjorn Olesen (DEN) 71-65
137 - Peter Hanson (SWE) 66-71, Martin Kaymer (GER) 68-69, Ian Poulter (ENG) 69-68, Prom Meesawat (THA) 67-70, Lee Westwood (ENG) 70-67
138 - Thongchai Jaidee (THA) 70-68, Bubba Watson (USA) 66-72, Gonzalo Fernandez-Castano (ESP) 71-67, Wu Ashun (CHN) 68-70, Carl Pettersson (SWE) 70-68
139 - Keegan Bradley (USA) 71-68, Jang Ik-Jae (KOR) 68-71
Selected:
140 - Paul Lawrie (SCO) 69-71
142 - Justin Rose (ENG) 72-70
143 - Francesco Molinari (ITA) 74-69, Brandt Snedeker (USA) 72-71
144 - Nick Watney (USA) 72-72
146 - Graeme McDowell (NIR) 71-75, Nicolas Colsaerts (BEL) 73-73
149 - Johnson Wagner (USA) 75-74