Yang took early control against the fifth-seeded Briton with three birdies in the first four holes and held off a late fightback before ending the match with a chip-in for birdie at the par-three 16th.
However, the Northern Irishman was able to celebrate reaching the third round for the first time in five appearances and will move past Tiger Woods in next week's world rankings.
Yang, who overhauled Woods to claim his first major title at the 2009 PGA Championship, will next meet Matt Kuchar, who beat fellow American Rickie Fowler 2&1.
German world number two Martin Kaymer, the second seed, came from two down after 12 holes to beat American Hunter Mahan 2&1 in a high-quality encounter on Friday.
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