Brian Bateman matched Yang's 75 Friday and he shares second place with Padraig Harrington (77) at 1-under-par 143. Carlos Franco was one of four players to post a round of 1-over 73 to share low round of the day honors. He shares fourth place with Trevor Immelman (74) and Kevin Na (74) at even-par 144.
Players battled windy and cold conditions Friday. Temperatures climbed only into the mid-40s and winds gusted over 20 mph. Arron Oberholser and Franco had the steadiest rounds with one birdie and two bogeys.
Yang, who began the day one shot behind overnight leader Ted Purdy, stumbled to a double bogey at the par-5 third. He tripped to another bogey at the fifth to drop to minus-3.
The Korean regained a pair of those lost strokes and took the lead with an eagle at the par-5 seventh. Yang moved back to even-par for his round when he rolled in a birdie putt at the par-4 10th.
Yang, a two-time winner in Japan in 2004, faltered to a bogey at the 11th to slip back to minus-5. He closed with bogeys at 16 and 18 to fall back to minus-3.
Harrington, despite bogeys at the first and fifth, took over the lead from Purdy. Harrington's slide continued with bogeys at the seventh and ninth to drop back to minus-2 and out of the lead.
Around the turn, the Irishman rolled off five straight pars. Harrington regained one lost stroke with a birdie at the par-5 15th. However, he tripped to a bogey at the next and another at the last to close at minus-1.
Bateman started three strokes off the pace, but bogeyed one and four to slip back to 2 under. After five straight pars, he dropped another stroke at the 10th at Jungmun Golf Club.
The 31-year-old Bateman turned things around with birdies at the 11th and 13th to get back to 3 under. He tripped to bogeys at the 15th and 18th to share second place.
Oberholser posted a 1-over 73. He shares seventh place with Spaniard Miguel Angel Jimenez (75) at 1-over-par 145. J.J. Henry and Cameron Beckman each posted rounds of 1-over 73. They are tied for 10th place with Matt Kuchar and Mark Calcavecchia are plus-2.
Daniel Chopra, Joe Ogilvie and Tim Petrovic are one stroke further back at 3-over-par 147.
Purdy, the first-round leader, slid all the way into a tie for 17th at 5-over-par 149 after a second-round, 12-over 84.