Wu, who is seeking a second victory in his national Open after lifting the title in 2015, carded eight birdies and a solitary bogey in his 65 and said: "It was a great day again today. I hit a lot of quality shots today and made a lot of birdies. I'm very happy.
"I hit a bad tee shot on five and I had a headache there again because I made a bogey there yesterday too. During the season break I took some time off to evaluate my game. I made some swing changes and it got better and better."
Spain's Jorge Campillo, who is seeking back-to-back victories after claiming his maiden European Tour title in Morocco last week, is three shots off the pace following a 69, with France's Victor Dubuisson part of a six-strong group two strokes further back.