Arron Oberholser managed a 2-under 70 to move into second place at 1-under-par 215. Brian Bateman shares third place with Kevin Na at even-par 216. Daniel Chopra and J.J. Henry are two strokes further back at plus-2.
Jimenez began the day four strokes behind second-round leader Yong-Eun Yang. The Spaniard tripped to a bogey at the first. Jimenez quickly atoned for that error with birdies at two and three to get back to even-par for the tournament.
The 40-year-old Jimenez stumbled to a another bogey at the fourth. However, it was his play around the turn that gave him the lead. The 11-time winner on the European Tour rolled in a birdie at No. 8 at Jungmun Golf Club.
Jimenez came right back to birdie the ninth to get to 1 under. He then birdied the par-5 11th for the third straight round.
The two-time Ryder Cup performer climbed to 3 under and a comfortable lead when he birdied the 14th. Jimenez, however, faltered to a bogey at 16 as his lead dropped to one. He parred his final two holes to remain there.
Oberholser was tied at plus-1 with Jimenez to begin the day. He fell further off the pace with bogeys at four and seven. The 29-year-old responded with birdies at Nos. 8 and 10 to get back to plus-1.
The two-time winner on the Nationwide Tour kept on rolling. Oberholser birdied the 14th and made it two straight when he birdied 15. He closed with three straight pars to remain at minus-1.
Joe Ogilvie and Tim Petrovic each carded rounds of even-par 72. They share seventh place with Irishman Padraig Harrington (76) at 3-over-par 219.
Mathias Gronberg used a 1-under 71 to move to 4-over-par 220. He is joined there by Matt Kuchar (74) and Carlos Franco (76).
Second-round leader Yong-Eun Yang fell all the way to plus-5 with an 8-over 80.