Teenage amateur Hu Mu carded a five-under-par 65 to open up a two-stroke lead after the second round of the Dell Championship.
The 18-year-old, who had considered withdrawing on the eve of the tournament due to illness, shot five birdies on the front nine without dropping a shot.
He later bogeyed the 12th before picking up another shot on the 17th to lead Yuan Hao and Wu Weihuang, who both carded 68s.