Sungjae Im made a lightning start to move two shots ahead midway through round two of the WGC-HSBC Champions.
World Number Two Rory McIlroy had made four birdies in a row to open up a two shot advantage at Sheshan International Golf Club but Im started his round with four of his own to get to ten under after five holes.
McIlroy turned in 33 to sit at eight under alongside fellow Open Champion Louis Oosthuizen and local hero Li Haotong.
The four time Major Champion started slowly on day one before coming home in 31 and quickly picked up where he had left off.
A spun approach to close range at the third brought a first birdie of the day and a long putt on the fourth had him within one of the lead.
Li found water on the sixth for a bogey and there was a five way tie for the lead but McIlroy soon burst out of it.
He made an eight foot left to righter on the fifth and the putt on the next went the other way from 12 feet to move him two ahead.
The Northern Irishman soon had company at the top, however, as Im started his round with three birdies to also get to nine under.
The duo were briefly two clear but Li hit an excellent third into the eighth after laying up and he was back where he started the day at eight under.
Oosthuizen sandwiched a bogey on the second with birdies on the first and third and added two more at the seventh and eighth to turn in 33.
He found sand off the 11th tee but hit a stunning second to set up a fifth birdie of the day and he was alongside Li at eight under.
But that was soon two back as Im's hot start continued with a 12 footer on the fourth for four in a row.
McIlroy then found the rough off the tee at the very difficult ninth and dropped a first shot of the day.
Matthew Fitzpatrick and Victor Perez were at seven under, a shot clear of Robert MacIntyre, Justin Rose and Adam Scott.